Absorbent structure

ABSTRACT

An absorbent structure comprising one or more absorbent layers wherein the absorbent structure exhibits a first cycle Peak Force compression between about 30 grams and about 150 grams. The absorbent structure further exhibits a fifth cycle dry recovery energy between 0.1 mJ and 2.8 mJ.

FIELD OF THE INVENTION

The present invention relates to absorbent structures useful inabsorbent articles such as diapers, incontinent briefs, training pants,diaper holders and liners, sanitary hygiene garments, and the like.Specifically, the present invention relates to an absorbent structurethat exhibits desirable consumer properties.

BACKGROUND OF THE INVENTION

Absorbent articles for the absorption of fluids aim to be comfortable tothe consumer. This traditionally represents the use of thinner materialswhile increasing absorption. Increased comfort may also be achievedthrough the use of channels and cuts into the absorbent core to createflexible zones that may include removing parts of the absorbent core. Agoal of increased comfort is to create an absorbent article that isgarment-like to the consumer while still protecting the consumer.

Traditionally, as a consumer wears an absorbent product and fluid entersthe product the structural properties of the absorbent core and productchange and degrade. This is because, the material will traditionallyeither lose its structural integrity or become less flexible, bunchtogether and unable to retain its shape as it absorbs the fluid,dependent upon the composition of the absorbent article. Further, manyabsorbent products may become more noticeable, with wearing, to theconsumer making them aware that they are using an absorbent product andthat the product is changing and may no longer function as well as itoriginally did.

The loss of structural integrity or loss of flexibility or inability tomaintain shape and compression recovery leads to a tradeoff betweencomfort and protection. Absorbent core structures that loss structuralintegrity tend to lose wet resiliency leading to a loss of consumerconfidence in the products ability to protect and absorb. Absorbentcores that lose flexibility due to their composition may becomeuncomfortable as they are no longer garment like. Hence, there exists aneed to create an absorbent core that balances comfort with protectionsuch that it may handle subsequent insults without the consumer feelingthat the product will not protect them and/or be uncomfortable to use.

The response of an absorbent structure (or article) to body inducedmechanical compression while wearing is referred to as its bunchedcompression response. Bunched compression can be an important factorwith regard to the overall comfort associated with wearing an absorbentarticle. Ideally measuring the Bunched compression response would allowone to determine peak forces required to compress an absorbent structureas well as determine the stored energy available to drive a productsshape recovery or “Energy of Recovery” following a compression of thearticle when in use With regard to bunched compression of an absorbentstructure during wear, it can be difficult to predict all the possiblemovements and positions that the consumer will make while using theabsorbent article. These can impact whether the consumer feels theabsorbent article and/or finds the absorbent article comfortable. It istherefore desired to develop a method for evaluating the bunchedcompression response of an absorbent article or portions of an absorbentarticle or an absorbent core structure that provides an indication as tothe compression of the absorbent article during wear.

Further, there exists a need to create an absorbent structure that issufficiently flexible before use and is still capable of maintaining itsstructural integrity after multiple insults as exhibited by theabsorbent structure's recovery energy after multiple test cycles.

Further, there exists a need to create a method for the creation of anabsorbent structure that becomes or maintains its flexibility whileabsorbing the fluids therefore allowing one to model the productaccording to the consumer's needs.

SUMMARY OF THE INVENTION

An absorbent structure comprising one or more absorbent layers whereinthe absorbent structure exhibits a first cycle Peak Force compressionbetween about 30 grams and about 150 grams is described. The absorbentstructure further exhibits a fifth cycle dry recovery energy between 0.1mJ and 2.8 mJ.

An absorbent structure comprising one or more absorbent layers whereinthe absorbent structure exhibits a first cycle Peak Force compressionbetween about 30 grams and about 150 grams is described. The absorbentstructure further exhibits a fifth cycle dry recovery energy between 0.1mJ and 2.8 mJ and a fifth cycle wet recovery energy between 0.6 mJ and5.0 mJ.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the invention can be more readily understood from thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a top view of an absorbent article.

FIG. 2 is a cross section view of the absorbent article of FIG. 1 takenalong line 2-2.

FIG. 3 is a cross section view of the absorbent article of FIG. 1 takenalong line 3-3.

FIG. 4 is a top view of an absorbent article.

FIG. 5 is a cross section view of the absorbent article of FIG. 4 takenalong line 5-5.

FIG. 6 is a cross section view of the absorbent article of FIG. 4 takenalong line 6-6.

FIG. 7 is a cross section view of the absorbent article of FIG. 4 takenalong line 7-7.

FIG. 8 is a magnified view of a portion of FIG. 5.

FIG. 9 is a top view of an absorbent article.

FIG. 10 is a cross section view of the absorbent article of FIG. 9 takenalong line 10-10.

FIG. 11 is a cross section view of the absorbent article of FIG. 9 takenalong line 11-11.

FIG. 12 is an SEM of a representative HIPE foam piece.

FIG. 13 is a magnified view of the SEM of FIG. 12.

FIG. 14 is a cross section view of the SEM of FIG. 12.

FIG. 15 is an SEM of a heterogeneous mass having an open-cell foampiece.

FIG. 16 is a magnified view of a portion of FIG. 15.

FIG. 17 is a top view image of a heterogeneous mass.

FIG. 18 is a schematic view of the equipment to perform the BunchCompression test.

FIGS. 19a-b are a schematic view of the equipment to perform the BunchCompression test.

FIGS. 20a-b is a representative curve from the Bunch Compression testmethod.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “bicomponent fibers” refers to fibers whichhave been formed from at least two different polymers extruded fromseparate extruders but spun together to form one fiber. Bicomponentfibers are also sometimes referred to as conjugate fibers ormulticomponent fibers. The polymers are arranged in substantiallyconstantly positioned distinct zones across the cross-section of thebicomponent fibers and extend continuously along the length of thebicomponent fibers. The configuration of such a bicomponent fiber maybe, for example, a sheath/core arrangement wherein one polymer issurrounded by another, or may be a side-by-side arrangement, a piearrangement, or an “islands-in-the-sea” arrangement.

As used herein, the term “biconstituent fibers” refers to fibers whichhave been formed from at least two polymers extruded from the sameextruder as a blend. Biconstituent fibers do not have the variouspolymer components arranged in relatively constantly positioned distinctzones across the cross-sectional area of the fiber and the variouspolymers are usually not continuous along the entire length of thefiber, instead usually forming fibrils which start and end at random.Biconstituent fibers are sometimes also referred to as multiconstituentfibers.

In the following description the term “cellulose fibers” is used.Cellulose fibers comprise naturally occurring fibers based on cellulose,such as, for example cotton, linen, etc. Wood pulp fibers are oneexample of cellulose fibers according to the present invention. Man-madefibers derived from cellulose, such as regenerated cellulose, e.g.viscose or partially or fully acetylated cellulose derivatives (e.g.cellulose acetate or triacetate), are also considered as cellulosefibers according to the present invention.

The term “disposable” is used herein to describe articles, which are notintended to be laundered or otherwise restored or reused as an article(i.e. they are intended to be discarded after a single use and possiblyto be recycled, composted or otherwise disposed of in an environmentallycompatible manner). The absorbent article comprising an absorbentstructure according to the present invention can be for example asanitary napkin, a panty liner, an adult incontinence product, a diaper,or any other product designed to absorb a bodily exudate. The absorbentstructure of the present invention will be herein described in thecontext of a typical absorbent article, such as, for example, a sanitarynapkin. Typically, such articles can comprise a liquid pervioustopsheet, a backsheet and an absorbent core intermediate the topsheetand the backsheet.

As used herein, an “enrobeable element” refers to an element that may beenrobed by the foam. The enrobeable element may be, for example, afiber, a group of fibers, a tuft, or a section of a film between twoapertures. It is understood that other elements are contemplated by thepresent invention.

A “fiber” as used herein, refers to any material that can be part of afibrous structure. Fibers can be natural or synthetic. Fibers can beabsorbent or non-absorbent.

A “fibrous structure” as used herein, refers to materials which can bebroken into one or more fibers. A fibrous structure can be absorbent oradsorbent. A fibrous structure can exhibit capillary action as well asporosity and permeability.

As used herein, the term “immobilize” refers to the reduction or theelimination of movement or motion.

As used herein, the term “meltblowing” refers to a process in whichfibers are formed by extruding a molten thermoplastic material through aplurality of fine, usually circular, die capillaries as molten threadsor filaments into converging high velocity, usually heated, gas (forexample air) streams which attenuate the filaments of moltenthermoplastic material to reduce their diameter. Thereafter, themeltblown fibers are carried by the high velocity gas stream and aredeposited on a collecting surface, often while still tacky, to form aweb of randomly dispersed meltblown fibers.

As used herein, the term “monocomponent” fiber refers to a fiber formedfrom one or more extruders using only one polymer. This is not meant toexclude fibers formed from one polymer to which small amounts ofadditives have been added for coloration, antistatic properties,lubrication, hydrophilicity, etc. These additives, for example titaniumdioxide for coloration, are generally present in an amount less thanabout 5 weight percent and more typically about 2 weight percent.

As used herein, the term “non-round fibers” describes fibers having anon-round cross-section, and includes “shaped fibers” and “capillarychannel fibers.” Such fibers can be solid or hollow, and they can betri-lobal, delta-shaped, and may be fibers having capillary channels ontheir outer surfaces. The capillary channels can be of variouscross-sectional shapes such as “U-shaped”, “H-shaped”, “C-shaped” and“V-shaped”. One practical capillary channel fiber is T401, designated as4DG fiber available from Fiber Innovation Technologies, Johnson City,Tenn. T-401 fiber is a polyethylene terephthalate (PET polyester).

As used herein, the term “nonwoven web” refers to a web having astructure of individual fibers or threads which are interlaid, but notin a repeating pattern as in a woven or knitted fabric, which do nottypically have randomly oriented fibers. Nonwoven webs or fabrics havebeen formed from many processes, such as, for example, electro-spinning,meltblowing processes, spunbonding processes, spunlacing processes,hydroentangling, airlaying, and bonded carded web processes, includingcarded thermal bonding. The basis weight of nonwoven fabrics is usuallyexpressed in grams per square meter (gsm). The basis weight of thelaminate web is the combined basis weight of the constituent layers andany other added components. Fiber diameters are usually expressed inmicrons; fiber size can also be expressed in denier, which is a unit ofweight per length of fiber. The basis weight of laminate webs suitablefor use in an article of the present invention can range from about 10gsm to about 100 gsm, depending on the ultimate use of the web.

As used herein, the term “peak force” relates to an indicator of theflexibility of the absorbent structure during compression. A lower “peakforce” represents a more flexible absorbent structure or absorbentproduct.

As used herein, the term “polymer” generally includes, but is notlimited to, homopolymers, copolymers, such as for example, block, graft,random and alternating copolymers, terpolymers, etc., and blends andmodifications thereof. In addition, unless otherwise specificallylimited, the term “polymer” includes all possible geometricconfigurations of the material. The configurations include, but are notlimited to, isotactic, atactic, syndiotactic, and random symmetries.

As used herein, the term “recovery energy” relates to an indicator ofhow well an absorbent structure or absorbent product can retain orregain is original shape. More specifically, “recovery energy” is ameasure of the amount of work the absorbent structure or the absorbentproduct will perform against the consumer's body and/or garmentfollowing compression.

Without being bound by theory, the upper limit for recovery energyshould be the compressive energy i.e. a fully recovered product whenremoved from the consumer's body/garment. Dry recovery energy forbetween 1 and 20 cycles should be less than 250% the dry compressiveenergy of a new product.

As used herein, “spunbond fibers” refers to small diameter fibers whichare formed by extruding molten thermoplastic material as filaments froma plurality of fine, usually circular capillaries of a spinneret withthe diameter of the extruded filaments then being rapidly reduced.Spunbond fibers are generally not tacky when they are deposited on acollecting surface. Spunbond fibers are generally continuous and haveaverage diameters (from a sample size of at least 10 fibers) larger than7 microns, and more particularly, between about 10 and 40 microns.

As used herein, a “test cycle” refers to a cycle of the BunchedCompression test.

As used herein, a “strata” or “stratum” relates to one or more layerswherein the components within the stratum are intimately combinedwithout the necessity of an adhesive, pressure bonds, heat welds, acombination of pressure and heat bonding, hydro-entangling,needlepunching, ultrasonic bonding, or similar methods of bonding knownin the art such that individual components may not be wholly separatedfrom the stratum without affecting the physical structure of the othercomponents. The skilled artisan should understand that while separatebonding is unnecessary between the strata, bonding techniques could beemployed to provide additional integrity depending on the intended use.

As used herein, a “tuft” or chad relates to discrete integral extensionsof the fibers of a nonwoven web. Each tuft can comprise a plurality oflooped, aligned fibers extending outwardly from the surface of the web.Each tuft can comprise a plurality of non-looped fibers that extendoutwardly from the surface of the web. Each tuft can comprise aplurality of fibers which are integral extensions of the fibers of twoor more integrated nonwoven webs.

As used herein, a “usage cycle” relates to the duration of use of theabsorbent structure as it transitions from a dry state to a saturatedwet state.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and 5 modifications can be made withoutdeparting from the spirit and scope of the invention.

GENERAL SUMMARY

The present invention relates to an absorbent structure that is flexibleand maintains its resiliency while in use. The absorbent structure alsoincreases in volume by less than 250% during the usage cycle, thereforeachieving a flexible product that maintains resiliency, bulk, andcomfort during a usage cycle.

The absorbent structure may comprise one or more absorbent layers. Theabsorbent structure may be a heterogeneous mass. In an embodiment, theabsorbent core structure is a two layer system wherein the upper layeris heterogeneous mass layer comprising one or more enrobeable elementsand one or more discrete open-cell foam pieces. The upper layerheterogeneous mass layer may be a stratum as defined above. The lowerlayer is an absorbent layer that comprises superabsorbent polymer. Theabsorbent core structure may comprise additional layers below theabsorbent layer that comprises superabsorbent polymer.

The absorbent core structure may comprise a heterogeneous mass layer asthose described in U.S. patent application No. 61/988,565, filed May 5,2014; U.S. patent application No. 62/115,921, filed Feb. 13, 2015; orU.S. patent application No. 62/018,212. The heterogeneous mass layer hasa depth, a width, and a height.

The absorbent structure may comprise an absorbent core or absorbent coreelements such 20 as those described in U.S. Pat. No. 8,263,820 issuedSep. 11, 2012 and U.S. Pat. No. 8,124,827 issued Feb. 28, 2012.

The absorbent structure may have a substrate layer. The substrate layerof the absorbent structure may advantageously comprise a fibrousmaterial substantially free of cellulose fibers. By saying that a layerof the absorbent core is “substantially free” of cellulose fibers, it ismeant in the context of the present invention that the layer should notcomprise any significant amount of cellulose fibers within its innerstructure. While cellulose fibers which may be present at an outersurface of the specified layer, for example at the interface between thespecified layer and an adjacent one, which could be for example an outerlayer wrapping the core 28, in some cases may accidentally and slightlypenetrate the structure of the specified layer, such shall not beconsidered significant. Significant amounts may correspond to less than10% by weight, less than 5% by weight, less than 3% by weight, or lessthan 1% by weight, based on the dry weight of the specified layer of theabsorbent core. The substrate layer 100 may also have a basis weightfrom 25 g/m2 to 120 g/m2, or from 35 g/m2 to 90 g/m2.

The absorbent structure may have a thermoplastic layer of thermoplasticmaterial. The thermoplastic material may comprise, in its entirety, asingle thermoplastic polymer or a blend of thermoplastic polymers,having a softening point, as determined by the ASTM Method D-36-95 “Ringand Ball”, in the range between 50° C. and 300° C., or alternatively thethermoplastic composition may be a hot melt adhesive comprising at leastone thermoplastic polymer in combination with other thermoplasticdiluents such as tackifying resins, plasticizers and additives such asantioxidants.

The thermoplastic polymer may have typically a molecular weight (Mw) ofmore than 10,000 and a glass transition temperature (Tg) usually belowroom temperature. Typical concentrations of the polymer in a hot meltare in the range of 20-40% by weight. A wide variety of thermoplasticpolymers may be suitable for use in the present invention. Suchthermoplastic polymers can be typically water insensitive. Exemplarypolymers can be (styrenic) block copolymers including A-B-A triblockstructures, A-B diblock structures and (A-B)n radial block copolymerstructures wherein the A blocks can be non-elastomeric polymer blocks,typically comprising polystyrene, and the B blocks can be unsaturatedconjugated diene or (partly) hydrogenated versions of such. The B blockcan be typically isoprene, butadiene, ethylene/butylene (hydrogenatedbutadiene), ethylene/propylene (hydrogenated isoprene), and mixturesthereof.

Other suitable thermoplastic polymers that may be employed aremetallocene polyolefins, which are ethylene polymers prepared usingsingle-site or metallocene catalysts. Therein, at least one comonomercan be polymerized with ethylene to make a copolymer, terpolymer orhigher order polymer. Also applicable can be amorphous polyolefins oramorphous polyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alphaolefins.

The resin can typically have a Mw below 5,000 and a Tg usually aboveroom temperature, typical concentrations of the resin in a hot melt canbe in the range of 30-60%. The plasticizer has a low Mw of typicallyless than 1,000 and a Tg below room temperature, a typical concentrationis 0-15%.

The thermoplastic material, typically a hotmelt adhesive, can be presentin the form of fibers throughout the core, being provided with knownmeans, i.e. the adhesive can be fiberized. Typically, the fibers canhave an average thickness of 1-100 micrometer and an average length of 5mm to 50 cm. In particular the layer of thermoplastic material,typically e.g. a hot melt adhesive, can be provided such as to comprisea net-like structure.

To improve the adhesiveness of the thermoplastic material to thesubstrate layer or to any other layer, in particular any other non-wovenlayer, such layers may be pre-treated with an auxiliary adhesive.

The absorbent structure may have absorbent polymer material. Withoutwishing to be bound by theory it is believed that such material, even inthe swollen state, i.e. when liquid has been absorbed, does notsubstantially obstruct the liquid flow throughout the material,particularly when further the permeability of said material, asexpressed by the saline flow conductivity (SFC) of the absorbent polymermaterial, is greater than 10, 20, 30 or 40 SFC-units, where 1 SFC unitis 1×10−7 (cm3×s)/g. Saline flow conductivity is a parameter wellrecognized in the art and is to be measured in accordance with the testdisclosed in EP 752 892 B.

The absorbent structure may be a heterogeneous mass. The heterogeneousmass has a depth, a width, and a height. The absorbent structure may beused as any part of an absorbent article including, for example, a partof an absorbent core, as an absorbent core, and/or as a topsheet forabsorbent articles such as sanitary napkins, panty liners, tampons,interlabial devices, wound dressings, diapers, adult incontinencearticles, and the like, which are intended for the absorption of bodyfluids, such as menses or blood or vaginal discharges or urine. Theabsorbent structure may be used in any product utilized to absorb andretain a fluid including surface wipes. The absorbent structure may beused as a paper towel. Exemplary absorbent articles in the context ofthe present invention are disposable absorbent articles.

The absorbent structure may be a heterogeneous mass comprisingenrobeable elements and one or more portions of foam pieces. Thediscrete portions of foam pieces are open-celled foam. The foam may be aHigh Internal Phase Emulsion (HIPE) foam.

The absorbent structure may be an absorbent core for an absorbentarticle wherein the absorbent core comprises a heterogeneous masscomprising fibers and one or more discrete portions of foam that areimmobilized in the heterogeneous mass.

In the following description of the invention, the surface of thearticle, or of each component thereof, which in use faces in thedirection of the wearer is called wearer-facing surface. Conversely, thesurface facing in use in the direction of the garment is calledgarment-facing surface. The absorbent article of the present invention,as well as any element thereof, such as, for example the absorbent core,has therefore a wearer-facing surface and a garment-facing surface.

The present invention relates to an absorbent structure that containsone or more discrete open-cell foam pieces foams that are integratedinto a heterogeneous mass comprising one or more enrobeable elementsintegrated into the one or more open-cell foams such that the two may beintertwined.

The open-cell foam pieces may comprise between 1% of the heterogeneousmass by volume to 99% of the heterogeneous mass by volume, such as, forexample, 5% by volume, 10% by volume, 15% by volume, 20% by volume, 25%by volume, 30% by volume, 35% by volume, 40% by volume, 45% by volume,50% by volume, 55% by volume, 60% by volume, 65% by volume, 70% byvolume, 75% by volume, 80% by volume, 85% by volume, 90% by volume, or95% by volume.

The heterogeneous mass may have void space found between the enrobeableelements, between the enrobeable elements and the enrobed elements, andbetween enrobed elements. The void space may contain a gas such as air.The void space may represent between 1% and 95% of the total volume fora fixed amount of volume of the heterogeneous mass, such as, forexample, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%,70%, 75%, 80%, 85%, 90% of the total volume for a fixed amount of volumeof the heterogeneous mass.

The combination of open-cell foam pieces and void space within theheterogeneous mass may exhibit an absorbency of between 10 g/g to 200g/g of the, such as for example, between 20 g/g and 190 g/g of theheterogeneous mass, such as, for example 30 g/g, 40 g/g, 60 g/g, 80 g/g,100 g/g, 120 g/g, 140 g/g 160 g/g 180 g/g or 190 g/g of theheterogeneous mass. Absorbency may be quantified according to the EDANANonwoven Absorption method 10.4-02.

The open-cell foam pieces are discrete foam pieces intertwined withinand throughout a heterogeneous mass such that the open-cell foam enrobesone or more of the enrobeable elements such as, for example, fiberswithin the mass. The open-cell foam may be polymerized around theenrobeable elements.

A discrete open-cell foam piece may enrobe more than one enrobeableelement. The enrobeable elements may be enrobed together as a bunch.Alternatively, more than one enrobeable element may be enrobed by thediscrete open-cell foam piece without contacting another enrobeableelement.

A discrete open-cell foam piece may be immobilized such that thediscrete open-cell foam piece does not change location within theheterogeneous mass during use of the absorbent structure.

A plurality of discrete open-cell foams may be immobilized such that thediscrete open-cell foam pieces do not change location within theheterogeneous mass during use of the absorbent structure.

One or more discrete foam pieces may be immobilized within theheterogeneous mass such that the one or more discrete foam pieces do notchange location after being spun at 300 rotations per minute for 30seconds.

The open-cell foam pieces may be discrete. Open-cell foam pieces areconsidered discrete in that they are not continuous throughout theentire heterogeneous mass. Not continuous throughout the entireheterogeneous mass represents that at any given point in theheterogeneous mass, the open-cell absorbent foam is not continuous in atleast one of the cross sections of a longitudinal, a vertical, and alateral plane of the heterogeneous mass. The absorbent foam may or maynot be continuous in the lateral and the vertical planes of the crosssection for a given point in the heterogeneous mass. The absorbent foammay or may not be continuous in the longitudinal and the vertical planesof the cross section for a given point in the heterogeneous mass. Theabsorbent foam may or may not be continuous in the longitudinal and thelateral planes of the cross section for a given point in theheterogeneous mass.

When the open-cell foam is not continuous in at least one of the crosssections of the longitudinal, the vertical, and the lateral plane of theheterogeneous mass, one or both of either the enrobeable elements or theopen-cell foam pieces may be bi-continuous throughout the heterogeneousmass.

The open-cell foam pieces may be located at any point in theheterogeneous mass. A foam piece may be surrounded by the elements thatmake up the enrobeable elements. A foam piece may be located on theouter perimeter of the heterogeneous mass such that only a portion ofthe foam piece is entangled with the elements of the heterogeneous mass.

The open-cell foam pieces may expand upon being contacted by a fluid toform a channel of discrete open-cell foam pieces. The open-cell foampieces may or may not be in contact prior to being expanded by a fluid.

An open-celled foam may be integrated onto the enrobeable elements priorto being polymerized. The open-cell foam pieces may be partiallypolymerized prior to being impregnated into or onto the enrobeableelements such that they become intertwined. After being impregnated intoor onto the enrobeable elements, the open-celled foam in either a liquidor solid state are polymerized to form one or more open-cell foampieces. The open-celled foam may be polymerized using any known methodincluding, for example, heat, UV, and infrared. Following thepolymerization of a water in oil open-cell foam emulsion, the resultingopen-cell foam is saturated with aqueous phase that needs to be removedto obtain a substantially dry open-cell foam. Removal of the saturatedaqueous phase or dewatering may occur using nip rollers, and vacuum.Utilizing a nip roller may also reduce the thickness of theheterogeneous mass such that the heterogeneous mass will remain thinuntil the open-cell foam pieces entwined in the heterogeneous mass areexposed to fluid.

Dependent upon the desired foam density, polymer composition, specificsurface area, or pore-size (also referred to as cell size), theopen-celled foam may be made with different chemical composition,physical properties, or both. For instance, dependent upon the chemicalcomposition, an open-celled foam may have a density of 0.0010 g/cc toabout 0.25 g/cc, or from 0.002 g/cc to about 0.2 g/cc, or from about0.005 g/cc to about 0.15 g/cc, or from about 0.01 g/cc to about 0.1g/cc, or from about 0.02 g/cc to about 0.08 g/cc, or about 0.04 g/cc.

Open-cell foam pore-sizes may range in average diameter of from 1 to 800μm, such as, for example, between 50 and 700 μm, between 100 and 600 μm,between 200 and 500 μm, between 300 and 400 μm.

The foam pieces may have a relatively uniform cell size. For example,the average cell size on one major surface may be about the same or varyby no greater than 10% as compared to the opposing major surface. Theaverage cell size of one major surface of the foam may differ from theopposing surface. For example, in the foaming of a thermosettingmaterial it is not uncommon for a portion of the cells at the bottom ofthe cell structure to collapse resulting in a lower average cell size onone surface. The cell size may be determined based upon the method foundbelow. The foams produced from the present invention are relativelyopen-celled. This refers to the individual cells or pores of the foambeing in substantially unobstructed communication with adjoining cells.The cells in such substantially open-celled foam structures haveintercellular openings or windows that are large enough to permit readyfluid transfer from one cell to another within the foam structure. Forpurpose of the present invention, a foam is considered “opencelled” ifat least about 80% of the cells in the foam that are at least 1 μm inaverage diameter size are in fluid communication with at least oneadjoining cell.

In addition to being open-celled, the foams may be sufficientlyhydrophilic to permit the foam to absorb aqueous fluids, for example theinternal surfaces of a foam may be rendered hydrophilic by residualhydrophilizing surfactants or salts left in the foam followingpolymerization, by selected post-polymerization foam treatmentprocedures (as described hereafter), or combinations of both.

For example when used in certain absorbent articles, an open-cell foammay be flexible and exhibit an appropriate glass transition temperature(Tg). The Tg represents the midpoint of the transition between theglassy and rubbery states of the polymer.

The Tg of a region may be less than about 200° C. for foams used atabout ambient temperature conditions, or less than about 90° C. The Tgmay be less than 50° C.

The open-cell foam pieces may be distributed in any suitable mannerthroughout the heterogeneous mass. The open-cell foam pieces may beprofiled along the vertical axis such that smaller pieces are locatedabove larger pieces. Alternatively, the pieces may be profiled such thatsmaller pieces are below larger pieces. The open-cell pieces may beprofiled along a vertical axis such that they alternate in size alongthe axis.

The open-cell foam pieces may be profiled along the longitudinal axissuch that smaller pieces are located in front of larger pieces.Alternatively, the pieces may be profiled such that smaller pieces arebehind larger pieces. The open-cell pieces may be profiled along alongitudinal axis such that they alternate in size along the axis. Theopen-cell foam pieces may be profiled along the lateral axis such thesize of the pieces goes from small to large or from large to small alongthe lateral axis. Alternatively, the open-cell pieces may be profiledalong a lateral axis such that they alternate in size along the axis.

The open-cell foam pieces may be profiled along any one of thelongitudinal, lateral, or vertical axis based on one or morecharacteristics of the open-cell foam pieces. Characteristics by whichthe open-cell foam pieces may be profiled within the heterogeneous massmay include, for example, absorbency, density, cell size, andcombinations thereof.

The open-cell foam pieces may be profiled along any one of thelongitudinal, lateral, or vertical axis based on the composition of theopen-cell foam. The open-cell foam pieces may have one compositionexhibiting desirable characteristics in the front of the heterogeneousmass and a different composition in the back of the heterogeneous massdesigned to exhibit different characteristics. The profiling of theopen-cell foam pieces may be either symmetric or asymmetric about any ofthe prior mentioned axes or orientations.

The open-cell foam pieces may be distributed along the longitudinal andlateral axis of the heterogeneous mass in any suitable form. Theopen-cell foam pieces may be distributed in a manner that forms a designor shape when viewed from a top planar view. The open-cell foam piecesmay be distributed in a manner that forms stripes, ellipticals, squares,or any other known shape or pattern.

The distribution may be optimized dependent on the intended use of theheterogeneous mass. For example, a different distribution may be chosenfor the absorption of aqueous fluids such as urine when used in a diaperor water when used in a paper towel versus for the absorption of aproteinaceous fluid such as menses. Further, the distribution may beoptimized for uses such as dosing an active or to use the foam as areinforcing element.

Different types of foams may be used in one heterogeneous mass. Forexample, some of the foam pieces may be polymerized HIPE while otherpieces may be made from polyurethane. The pieces may be located atspecific locations within the mass based on their properties to optimizethe performance of the heterogeneous mass.

The foam pieces may be similar in composition yet exhibit differentproperties. For example, using HIPE foam, some foam pieces may be thinuntil wet while others may have been expanded within the heterogeneousmass.

The foam pieces and enrobeable elements may be selected to complementeach other. For example, a foam that exhibits high permeability with lowcapillarity may enrobe an element that exhibits high capillarity to wickthe fluid through the heterogeneous mass. It is understood that othercombinations may be possible wherein the foam pieces complement eachother or wherein the foam pieces and enrobeable elements both exhibitsimilar properties.

Profiling may occur using more than one heterogeneous mass with eachheterogeneous mass having one or more types of foam pieces. Theplurality of heterogeneous masses may be layered so that the foam isprofiled along any one of the longitudinal, lateral, or vertical axisbased on one or more characteristics of the open-cell foam pieces for anoverall product that contains the plurality of heterogeneous masses.Further, each heterogeneous mass may have a different enrobeable elementto which the foam is attached. For example, a first heterogeneous massmay have foam particles enrobing a nonwoven while a second heterogeneousmass adjacent the first heterogeneous mass may have foam particlesenrobing a film or one surface of a film.

The open-cell foam may be made from a polymer formula that can includeany suitable thermoplastic polymer, or blend of thermoplastic polymers,or blend of thermoplastic and non-thermoplastic polymers.

Examples of polymers, or base resins, suitable for use in the foampolymer formula include styrene polymers, such as polystyrene orpolystyrene copolymers or other alkenyl aromatic polymers; polyolefinsincluding homo or copolymers of olefins, such as polyethylene,polypropylene, polybutylene, etc.; polyesters, such as polyalkyleneterephthalate; and combinations thereof. A commercially availableexample of polystyrene resin is Dow STYRON® 685D, available from DowChemical Company in Midland, Mich., U.S.A.

Coagents and compatibilizers can be utilized for blending such resins.Crosslinking agents can also be employed to enhance mechanicalproperties, foamability and expansion. Crosslinking may be done byseveral means including electron beams or by chemical crosslinkingagents including organic peroxides. Use of polymer side groups,incorporation of chains within the polymer structure to prevent polymercrystallization, lowering of the glass transition temperature, loweringa given polymer's molecular weight distribution, adjusting melt flowstrength and viscous elastic properties including elongational viscosityof the polymer melt, block copolymerization, blending polymers, and useof polyolefin homopolymers and copolymers have all been used to improvefoam flexibility and foamability. Homopolymers can be engineered withelastic and crystalline areas. Syndiotactic, atactic and isotacticpolypropylenes, blends of such and other polymers can also be utilized.Suitable polyolefin resins include low, including linear low, medium andhigh-density polyethylene and polypropylene, which are normally madeusing Ziegler-Natta or Phillips catalysts and are relatively linear;generally more foamable are resins having branched polymer chains.Isotactic propylene homopolymers and blends are made usingmetallocene-based catalysts. Olefin elastomers are included. Ethyleneand a-olefin copolymers, made using either Ziegler-Natta or ametallocene catalyst, can produce soft, flexible foam havingextensibility. Polyethylene cross-linked with aolefins and variousethylene ionomer resins can also be utilized. Use of ethyl-vinyl acetatecopolymers with other polyolefin-type resins can produce soft foam.Common modifiers for various polymers can also be reacted with chaingroups to obtain suitable functionality. Suitable alkenyl aromaticpolymers include alkenyl aromatic homopolymers and copolymers of alkenylaromatic compounds and copolymerizable ethylenically unsaturatedcomonomers including minor proportions of non-alkenyl aromatic polymersand blends of such. Ionomer resins can also be utilized.

Other polymers that may be employed include natural and syntheticorganic polymers including cellulosic polymers, methyl cellulose,polylactic acids, polyvinyl acids, polyacrylates, polycarbonates,starch-based polymers, polyetherimides, polyamides, polyesters,polymethylmethacrylates, and copolymer/polymer blends. Rubber-modifiedpolymers such as styrene elastomers, styrene/butadiene copolymers,ethylene elastomers, butadiene, and polybutylene resins,ethylene-propylene rubbers, EPDM, EPM, and other rubbery homopolymersand copolymers of such can be added to enhance softness and hand. Olefinelastomers can also be utilized for such purposes. Rubbers, includingnatural rubber, SBR, polybutadiene, ethylene propylene terpolymers, andvulcanized rubbers, including TPVs, can also be added to improverubber-like elasticity.

Thermoplastic foam absorbency can be enhanced by foaming withspontaneous hydrogels, commonly known as superabsorbents.Superabsorbents can include alkali metal salts of polyacrylic acids;polyacrylamides; polyvinyl alcohol; ethylene maleic anhydridecopolymers; polyvinyl ethers; hydroxypropylcellulose; polyvinylmorpholinone; polymers and copolymers of vinyl sulfonic acid,polyacrylates, polyacrylamides, polyvinyl pyridine; and the like. Othersuitable polymers include hydrolyzed acrylonitrile grafted starch,acrylic acid grafted starch, carboxy-methyl-cellulose, isobutylenemaleic anhydride copolymers, and mixtures thereof. Further suitablepolymers include inorganic polymers, such as polyphosphazene, and thelike. Furthermore, thermoplastic foam biodegradability and absorbencycan be enhanced by foaming with cellulose-based and starch-basedcomponents such as wood and/or vegetable fibrous pulp/flour.

In addition to any of these polymers, the foam polymer formula may also,or alternatively, include diblock, triblock, tetrablock, or othermulti-block thermoplastic elastomeric and/or flexible copolymers such aspolyolefin-based thermoplastic elastomers including random blockcopolymers including ethylene a-olefin copolymers; block copolymersincluding hydrogenated butadiene-isoprene-butadiene block copolymers;stereoblock polypropylenes; graft copolymers, includingethylene-propylene-diene terpolymer or ethylene-propylene-diene monomer(EPDM), ethylene-propylene random copolymers (EPM), ethylene propylenerubbers (EPR), ethylene vinyl acetate (EVA), and ethylene-methylacrylate (EMA); and styrenic block copolymers including diblock andtriblock copolymers such as styrene-isoprene-styrene (SIS),styrene-butadiene-styrene (SBS), styrene (SBS)styrene-isoprene-butadiene-styrene (SIBS),styreneethylene/butylene-styrene (SEBS), orstyrene-ethylene/propylene-styrene (SEPS), which may be obtained fromKraton Polymers of Belpre, Ohio, U.S.A., under the trade designationKRATON® elastomeric resin or from Dexco, a division of ExxonMobilChemical Company in Houston, Tex., U.S.A., under the trade designationVECTOR® (SIS and SBS polymers) or SEBS polymers as the SEPTON® series ofthermoplastic rubbers from Kuraray America, Inc. in New York, N.Y.,U.S.A.; blends of thermoplastic elastomers with dynamic vulcanizedelastomer-thermoplastic blends; thermoplastic polyether esterelastomers; ionomeric thermoplastic elastomers; thermoplastic elasticpolyurethanes, including those available from E.I. Du Pont de Nemours inWilmington, Del., U.S.A., under the trade name LYCRA® polyurethane, andESTANE® available from Noveon, Inc. in Cleveland, Ohio, U.S.A.;thermoplastic elastic polyamides, including polyether block amidesavailable from ATOFINA Chemicals, Inc. in Philadelphia, Pa., U.S.A.,under the trade name PEBAX® polyether block amide; thermoplastic elasticpolyesters, including those available from E.I. Du Pont de NemoursCompany, under the trade name HYTREL®, and ARNITEL® from DSM EngineeringPlastics of Evansville, Ind., U.S.A., and single-site ormetallocene-catalyzed polyolefins having a density of less than about0.89 grams/cubic centimeter such as metallocene polyethylene resins,available from Dow Chemical Company in Midland, Mich., U.S.A. under thetrade name AFFINITY™; and combinations thereof.

As used herein, a tri-block copolymer has an ABA structure where the Arepresents several repeat units of type A, and B represents severalrepeat units of type B. As mentioned above, several examples of styrenicblock copolymers are SBS, SIS, SIBS, SEBS, and SEPS. In these copolymersthe A blocks are polystyrene and the B blocks are the rubbery component.Generally these triblock copolymers have molecular weights that can varyfrom the low thousands to hundreds of thousands and the styrene contentcan range from 5% to 75% based on the weight of the triblock copolymer.A diblock copolymer is similar to the triblock but is of an ABstructure. Suitable diblocks include styrene-isoprene diblocks, whichhave a molecular weight of approximately one-half of the triblockmolecular weight and having the same ratio of A blocks to B blocks.Diblocks with a different ratio of A to B blocks or a molecular weightlarger or greater than one-half of triblock copolymers may be suitablefor improving the foam polymer formula for producing low-density, soft,flexible, absorbent foam via polymer extrusion.

Suitably, the foam polymer formula includes up to about 90%, by weight,of polystyrene, and at least 10%, by weight, of thermoplastic elastomer.More particularly, the foam polymer formula may include between about45% and about 90%, by weight, of polystyrene, and between about 10% andabout 55%, by weight, of thermoplastic elastomer. Alternatively, thefoam polymer formula may include between about 50% and about 80%, byweight, of polystyrene, and between about 20% and about 50%, by weight,of thermoplastic elastomer. For example, the foam polymer formula mayinclude equal amounts of polystyrene and thermoplastic elastomer.

The foam polymer formula may include about 40% to about 80% by weightpolystyrene and about 20% to about 60% by weight thermoplasticelastomer. The foam polymer formula may include about 50% to about 70%by weight polystyrene and about 30% to about 50% by weight thermoplasticelastomer.

A plasticizing agent can be included in the foam polymer formula. Aplasticizing agent is a chemical agent that imparts flexibility,stretchability and workability. The type of plasticizing agent has aninfluence on foam gel properties, blowing agent migration resistance,cellular structure, including the fine cell size, and number ofopen-cells. Typically plasticizing agents are of low molecular weight.The increase in polymer chain mobility and free volume caused byincorporation of a plasticizing agent typically results in a Tgdecrease, and plasticizing agent effectiveness is often characterized bythis measurement. Petroleum-based oils, fatty acids, and esters arecommonly used and act as external plasticizing agents or solventsbecause they do not chemically bond to the polymer yet remain intact inthe polymer matrix upon crystallization.

The plasticizing agent increases cell connectivity by thinning membranesbetween cells to the point of creating porous connections between cells;thus, the plasticizing agent increases open-cell content. Suitably, theplasticizing agent is included in an amount between about 0.5% and about10%, or between about 1% and about 10%, by weight, of the foam polymerformula. The plasticizing agent is gradually and carefully metered inincreasing concentration into the foam polymer formula during thefoaming process because too much plasticizing agent added at oncecreates cellular instability, resulting in cellular collapse.

Examples of suitable plasticizing agents include polyethylene, ethylenevinyl acetate, mineral oil, palm oil, waxes, esters based on alcoholsand organic acids, naphthalene oil, paraffin oil, and combinationsthereof. A commercially available example of a suitable plasticizingagent is a small-chain polyethylene that is produced as a catalyticpolymerization of ethylene; because of its low molecular weight it isoften referred to as a “wax.” This low-density, highly branchedpolyethylene “wax” is available from Eastman Chemical Company ofKingsport, Tenn., U.S.A., under the trade designation EPOLENE® C-10.

In order for the foam to be used in personal care and medical productapplications and many absorbent wiping articles and non-personal carearticles, the foam must meet stringent chemical and safety guidelines. Anumber of plasticizing agents are FDA-approved for use in packagingmaterials. These plasticizing agents include: acetyl tributyl citrate;acetyl triethyl citrate; p-tert-butylphenyl salicylate; butyl stearate;butylphthalyl butyl glycolate; dibutyl sebacate; di-(2-ethylhexyl)phthalate; diethyl phthalate; diisobutyl adipate; diisooctyl phthalate;diphenyl-2-ethylhexyl phosphate; epoxidized soybean oil; ethylphthalylethyl glycolate; glycerol monooleate; monoisopropyl citrate; mono-, di-,and tristearyl citrate; triacetin (glycerol triacetate); triethylcitrate; and 3-(2-xenyl)-1,2-epoxypropane.

The same material used as the thermoplastic elastomer may also be usedas the plasticizing agent. For example, the KRATON® polymers, describedabove, may be used as a thermoplastic elastomer and/or a plasticizingagent. In which case, the foam polymer formula may include between about10% and about 50%, by weight, of a single composition that acts as botha thermoplastic elastomer and a plasticizing agent. Described in analternative manner, the foam may be formed without a plasticizing agentper se; in which case, the foam polymer formula may include betweenabout 10% and about 50%, by weight, of the thermoplastic elastomer.

Foaming of soft, flexible polymers, such as thermoplastic elastomers, toa low density is difficult to achieve. The addition of a plasticizingagent makes foaming to low densities even more difficult to achieve. Themethod of the invention overcomes this difficulty through the inclusionof a surfactant in the foam polymer formula. The surfactant stabilizesthe cells, thereby counteracting cellular collapse while retaining anopen-cell structure. This stabilization of the cells creates celluniformity and control of cell structure. In addition to enablingfoaming of plasticized thermoplastic elastomer polymer containing foamformulations to low densities, the surfactant also provides wettabilityto enable the resulting foam to absorb fluid.

The foam pieces may be made from a thermoplastic absorbent foam such asa polyurethane foam. The thermoplastic foam may comprise surfactant andplasticizing agent. Polyurethane polymers are generally formed by thereaction of at least one polyisocyanate component and at least onepolyol component. The polyisocyanate component may comprise one or morepolyisocyanates. The polyol component may comprise one or more polyols.The concentration of a polyol may be expressed with regard to the totalpolyol component. The concentration of polyol or polyisocyanate mayalternatively be expressed with regard to the total polyurethaneconcentration. Various aliphatic and aromatic polyisocyanates have beendescribed in the art. The polyisocyanate utilized for forming thepolyurethane foam typically has a functionality between from 2 and 3.The functionality may be no greater than about 2.5.

The foam may be prepared from at least one aromatic polyisocyanate.Examples of aromatic polyisocyanates include those having a singlearomatic ring such as are toluene 2,4 and 2,6-diisocyanate (TDI) andnaphthylene 1,5-diisocyanate; as well as those having at least twoaromatic rings such as diphenylmethane 4,4′-, 2,4′- and2,2′-diisocyanate (MDI).

The foam may be prepared from one or more (e.g. aromatic) polymericpolyisocyanates. Polymeric polyisocyanates typically have a (weightaverage) molecular weight greater than a monomeric polyisocyanate(lacking repeating units), yet lower than a polyurethane prepolymer.Thus, the polyurethane foam is derived from at least one polymericpolyisocyanate that lacks urethane linkages. In other words, thepolyurethane foam is derived from a polymeric isocyanate that is not apolyurethane prepolymer. Polymeric polyisocyanates comprises otherlinking groups between repeat units, such as isocyanurate groups, biuretgroups, carbodiimide groups, uretonimine groups, uretdione groups, etc.as known in the art.

Some polymeric polyisocyanates may be referred to as “modified monomericisocyanate”. For example pure 4,4′-methylene diphenyl diisocyanate (MDI)is a solid having a melting point of 38° C. and an equivalent weight of125 g/equivalent. However, modified MDIs, are liquid at 38° C. and havea higher equivalent weight (e.g. 143 g/equivalent). The difference inmelting point and equivalent weight is believed to be a result of asmall degree of polymerization, such as by the inclusion of linkinggroups, as described above.

Polymeric polyisocyanates, including modified monomeric isocyanate, maycomprise a mixture of monomer in combination with polymeric speciesinclusive of oligomeric species. For example, polymeric MDI is reportedto contain 25-80% monomeric 4,4′-methylene diphenyl diisocyanate as wellas oligomers containing 3-6 rings and other minor isomers, such as 2,2′isomer.

Polymeric polyisocyanates typically have a low viscosity as compared toprepolymers. The polymeric isocyanates utilized herein typically have aviscosity no greater than about 300 cps at 25° C. and in someembodiments no greater than 200 cps or 100 cps at 25° C. The viscosityis typically at least about 10, 15, 20 or 25 cps at 25° C.

The equivalent weight of polymeric polyisocyanates is also typicallylower than that of prepolymers. The polymeric isocyanates utilizedherein typically have an equivalent weight of no greater than about 250g/equivalent and in some embodiments no greater than 200 g/equivalent or175 g/equivalent. In some embodiments, the equivalent weight is at least130 g/equivalent.

The average molecular weight (Mw) of polymeric polyisocyanates is alsotypically lower than that of polyurethane prepolymers. The polymericisocyanates utilized herein typically have an average molecular weight(Mw) of no greater than about 500 Da and in some embodiments no greaterthan 450, 400, or 350 Da. The polyurethane may be derived from a singlepolymeric isocyanate or a blend of polymeric isocyanates. Thus, 100% ofthe isocyanate component is polymeric isocyanate(s). A major portion ofthe isocyanate component may be a single polymeric isocyanate or a blendof polymeric isocyanates. In these embodiments, at least 50, 60, 70, 75,80, 85 or 90 wt-% of the isocyanate component is polymericisocyanate(s).

Some illustrative polyisocyanates include for example, polymeric MDIdiisocyanate from Huntsman Chemical Company, The Woodlands, Tex, underthe trade designation “RUBINATE 1245”; and modified MDI isocyanateavailable from Huntsman Chemical Company under the trade designation“SUPRASEC 9561”.

The aforementioned isocyanates are reacted with a polyol to prepare thepolyurethane foam material. The polyurethane foams are hydrophilic, suchthat the foam absorbs aqueous liquids, particularly body fluids. Thehydrophilicity of the polyurethane foams is typically provided by use ofan isocyanate-reactive component, such as a polyether polyol, having ahigh ethylene oxide content.

Examples of useful polyols include adducts [e.g., polyethylene oxide,polypropylene oxide, and poly(ethylene oxide-propylene oxide) copolymer]of dihydric or trihydric alcohols (e.g., ethylene glycol, propyleneglycol, glycerol, hexanetriol, and triethanolamine) and alkylene oxides(e.g., ethylene oxide, propylene oxide, and butylene oxide). Polyolshaving a high ethylene oxide content can also be made by othertechniques as known in the art. Suitable polyols typically have amolecular weight (Mw) of 100 to 5,000 Da and contain an averagefunctionality of 2 to 3.

The polyurethane foam is typically derived from (or in other words isthe reaction product of) at least one polyether polyol having ethyleneoxide (e.g. repeat) units. The polyether polyol typically has anethylene oxide content of at least 10, 15, 20 or 25 wt-% and typicallyno greater than 75 wt-%. Such polyether polyol has a higherfunctionality than the polyisocyanate. The average functionality may beabout 3. The polyether polyol typically has a viscosity of no greaterthan 1000 cps at 25° C. and in some embodiments no greater than 900,800, or 700 cps. The molecular weight of the polyether polyol istypically at least 500 or 1000 Da and in some embodiments no greaterthan 4000 or 3500, or 3000 Da. Such polyether polyol typically has ahydroxyl number of at least 125, 130, or 140. An illustrative polyolincludes for example a polyether polyol product obtained from theCarpenter Company, Richmond, Va. under the designation “CDB-33142POLYETHER POLYOL”, “CARPOL GP-5171”.

One or more polyether polyols having a high ethylene oxide content and amolecular weight (Mw) of no greater than 5500, or 5000, or 4500, or4000, or 3500, or 3000 Da, as just described, may be the primary or solepolyether polyols of the polyurethane foam. For example, such polyetherpolyols constitute at least 50, 60, 70, 80, 90, 95 or 100 wt-% of thetotal polyol component. Thus, the polyurethane foam may comprise atleast 25, 30, 35, 40, 45 or 50 wt-% of polymerized units derived fromsuch polyether polyols.

One or more polyether polyols having a high ethylene oxide content maybe utilized in combination with other polyols. The other polyols mayconstitute at least 1, 2, 3, 4, or 5 wt-% of the total polyol component.The concentration of such other polyols typically does not exceed 40, or35, or 30, or 25, or 20, or 15, or 10 wt-% of the total polyolcomponent, i.e. does not exceed 20 wt-%, or 17.5 wt-%, or 15 wt-%, or12.5 wt-%, or 10 wt-%, or 7.5 wt-%, or 5 wt-% of the polyurethane.Illustrative other polyols include a polyether polyol product (ChemicalAbstracts Number 25791-96-2) that can be obtained from the CarpenterCompany, Richmond, Va. under the designation “CARPOL GP-700 POLYETHERPOLYOL” and a polyether polyol product (Chemical Abstracts Number9082-00-2) that can be obtained from Bayer Material Science, Pittsburgh,Va. under the trade designation “ARCOL E-434”. Such optional otherpolyols may comprise polypropylene (e.g. repeat) units.

The polyurethane foam generally has an ethylene oxide content of atleast 10, 11, or 12 wt-% and no greater than 20, 19, or 18 wt-%. Thepolyurethane foam may have an ethylene oxide content of no greater than17 or 16 wt-%.

The kinds and amounts of polyisocyanate and polyol components areselected such that the polyurethane foam is relatively soft, yetresilient. These properties can be characterized for example byindentation force deflection and constant deflection compression set, asmeasured according to the test methods described in the examples. Thepolyurethane foam may have an indentation force deflection of less than75N at 50%. The indentation force deflection at 50% may be less than70N, or 65N, or 60 N. The polyurethane foam may have an indentationforce deflection of less than 100N at 65%. The indentation forcedeflection at 65% may be less than 90N, or 80N, or 70 N, or 65N, or 60N.The indentation force deflection at 50% or 65% may be typically at least30N or 35N. The constant deflection compression set at 50% deflectioncan be zero and is typically at least 0.5, 1 or 2% and generally nogreater than 35%. The constant deflection compression set at 50%deflection may be no greater than 30%, or 25%, or 20%, or 15%, or 10%.

The polyurethane foam may comprise known and customary polyurethaneformation catalysts such as organic tin compounds and/or an amine-typecatalyst. The catalysts may beused in an amount of from 0.01 to 5 wt-%of the polyurethane. The amine-type catalyst is typically a tertiaryamine Examples of suitable tertiary amine include monoamines such astriethylamine, and dimethyl cyclohexylamine; diamines such astetramethylethylenediamine, and tetramethylhexanediamine; triamines suchas tetramethylguanidine; cyclic amines such as triethylenediamine,dimethylpiperadine, and methylmorphorine; alcoholamines such asdimethylaminoethanol, trimethylaminoethylethanolamine, andhydroxyethylmorphorine; ether amines such as bisdimethylaminoethylethanol; diazabicycloalkenes such as 1,5-diazabicyclo(5,4,0)undecene-7(DBU), and 1,5-diazabicyclo(4,3,0)nonene-5; and organic acid salts ofthe diazabicycloalkenes such as phenol salt, 2-ethylhexanoate andformate of DBU. These amines can be used either singly or incombination. The amine-type catalyst can be used in an amount no greaterthan 4, 3, 2, 1 or 0.5 wt-% of the polyurethane.

The polyurethane typically comprises a surfactant to stabilize the foam.Various surfactants have been described in the art. A siliconesurfactant may be employed that comprises ethylene oxide (e.g. repeat)units, optionally in combination with propylene oxide (e.g. repeat)units such as commercially available from Air Products under the tradedesignation “DABCO DC-198”. The concentration of hydrophilic surfactantmay typically range from about 0.05 to 1 or 2 wt-% of the polyurethane.

The polyurethane foam may comprise various additives such as surfaceactive substances, foam stabilizers, cell regulators, blocking agents todelay catalytic reactions, fire retardants, chain extenders,crosslinking agents, external and internal mold release agents, fillers,pigments (titanium dioxide), colorants, optical brighteners,antioxidants, stabilizers, hydrolysis inhibitors, as well as anti-fungaland anti-bacteria substances. Such other additives are typicallycollectively utilized at concentrations ranging from 0.05 to 10 wt-% ofthe polyurethane.

The absorbent foam may be white in color. Certain hindered aminestabilizers can contribute to discoloration, such as yellowing, of theabsorbent foam. The absorbent foam may be free of diphenylaminestabilizer and/or phenothiazine stabilizer.

The absorbent foam may be a colored (i.e. a color other than white). Thewhite or colored absorbent foam can include a pigment in at least one ofthe components. Pigment may be combined with a polyol carrier and isadded to the polyol liquid stream during manufacture of the polyurethanefoam. Commercially available pigments include for example DispersiTech™2226 White, DispersiTech™ 2401 Violet, DispersiTech™ 2425 Blue,DispersiTech™ 2660 Yellow, and DispersiTech™ 28000 Red from Milliken inSpartansburg, S.C. and Pdi® 34-68020 Orange from Ferro in Cleveland,Ohio.

In the production of polyurethane foams, the polyisocyanate componentand polyol component are reacted such that an equivalence ratio ofisocyanate groups to the sum of hydroxyl groups is no greater than 1to 1. The components may be reacted such that there are excess hydroxylgroups (e.g. excess polyol). The equivalence ratio of isocyanate groupsto the sum of the hydroxy groups may be at least 0.7 to 1. For example,the ratio may be at least 0.75:1, or at least 0.8:1.

The hydrophilic (e.g. polyol(s)) component(s) of the (e.g. polyurethane)polymeric foam provide the desired absorption capacity of the foam. Thusthe foam may be free of superabsorbent polymer. Further, thepolyurethane foam is free of amine or imine complexing agent such asethylenimine, polyethylenimine, polyvinylamine, carboxy-methylatedpolyethylenimines, phosphono-methylated polyethylenimines, quaternizedpolyethylenimines and/or dithiocarbamitized polyethylenimines; asdescribed for example in U.S. Pat. Nos. 6,852,905 and 6,855,739.

The polymeric (e.g. polyurethane) foam typically has an average basisweight of at least 100, 150, 200, or 250 gsm and typically no greaterthan 500 gsm. The average basis weight may be no greater than 450, or400 gsm. The average density of the (e.g. polyurethane) polymeric foamis typically at least 3, 3.5 or 4 lbs/ft3 and no greater than 7 lbs/ft3.

The open-celled foam is a thermoset polymeric foam made from thepolymerization of a High Internal Phase Emulsion (HIPE), also referredto as a polyHIPE. To form a HIPE, an aqueous phase and an oil phase arecombined in a ratio between about 8:1 and 140:1. The aqueous phase tooil phase ratio may be between about 10:1 and about 75:1, and theaqueous phase to oil phase ratio may be between about 13:1 and about65:1. This is termed the “water-to-oil” or W:O ratio and can be used todetermine the density of the resulting polyHIPE foam. As discussed, theoil phase may contain one or more of monomers, comonomers,photoinitiators, crosslinkers, and emulsifiers, as well as optionalcomponents. The water phase may contain water and one or more componentssuch as electrolyte, initiator, or optional components.

The open-cell foam can be formed from the combined aqueous and oilphases by subjecting these combined phases to shear agitation in amixing chamber or mixing zone. The combined aqueous and oil phases aresubjected to shear agitation to produce a stable HIPE having aqueousdroplets of the desired size. An initiator may be present in the aqueousphase, or an initiator may be introduced during the foam making process,or after the HIPE has been formed. The emulsion making process producesa HIPE where the aqueous phase droplets are dispersed to such an extentthat the resulting HIPE foam will have the desired structuralcharacteristics. Emulsification of the aqueous and oil phase combinationin the mixing zone may involve the use of a mixing or agitation devicesuch as an impeller, by passing the combined aqueous and oil phasesthrough a series of static mixers at a rate necessary to impart therequisite shear, or combinations of both. Once formed, the HIPE can thenbe withdrawn or pumped from the mixing zone. One method for formingHIPEs using a continuous process is described in U.S. Pat. No. 5,149,720(DesMarais et al), issued Sep. 22, 1992; U.S. Pat. No. 5,827,909(DesMarais) issued Oct. 27, 1998; and U.S. Pat. No. 6,369,121 (Catalfamoet al.) issued Apr. 9, 2002.

The emulsion can be withdrawn or pumped from the mixing zone andimpregnated into or onto a mass prior to being fully polymerized. Oncefully polymerized, the foam pieces and the elements are intertwined suchthat discrete foam pieces are bisected by the elements comprising themass and such that parts of discrete foam pieces enrobe portions of oneor more of the elements comprising the heterogeneous mass.

Following polymerization, the resulting foam pieces are saturated withaqueous phase that needs to be removed to obtain substantially dry foampieces. Foam pieces may be squeezed free of most of the aqueous phase byusing compression, for example by running the heterogeneous masscomprising the foam pieces through one or more pairs of nip rollers. Thenip rollers can be positioned such that they squeeze the aqueous phaseout of the foam pieces. The nip rollers can be porous and have a vacuumapplied from the inside such that they assist in drawing aqueous phaseout of the foam pieces. Nip rollers may be positioned in pairs, suchthat a first nip roller is located above a liquid permeable belt, suchas a belt having pores or composed of a mesh-like material and a secondopposing nip roller facing the first nip roller and located below theliquid permeable belt. One of the pair, for example the first nip rollercan be pressurized while the other, for example the second nip roller,can be evacuated, so as to both blow and draw the aqueous phase out theof the foam. The nip rollers may also be heated to assist in removingthe aqueous phase. Nip rollers may be applied to non-rigid foams, thatis, foams whose walls would not be destroyed by compressing the foampieces.

In place of or in combination with nip rollers, the aqueous phase may beremoved by sending the foam pieces through a drying zone where it isheated, exposed to a vacuum, or a combination of heat and vacuumexposure. Heat can be applied, for example, by running the foam though aforced air oven, IR oven, microwave oven or radiowave oven. The extentto which a foam is dried depends on the application. Greater than 50% ofthe aqueous phase may be removed. Greater than 90%, and in still otherembodiments greater than 95% of the aqueous phase may be removed duringthe drying process.

Open-cell foam may be produced from the polymerization of the monomershaving a continuous oil phase of a High Internal Phase Emulsion (HIPE).The HIPE may have two phases. One phase is a continuous oil phase havingmonomers that are polymerized to form a HIPE foam and an emulsifier tohelp stabilize the HIPE. The oil phase may also include one or morephotoinitiators. The monomer component may be present in an amount offrom about 80% to about 99%, and in certain embodiments from about 85%to about 95% by weight of the oil phase. The emulsifier component, whichis soluble in the oil phase and suitable for forming a stablewater-in-oil emulsion may be present in the oil phase in an amount offrom about 1% to about 20% by weight of the oil phase. The emulsion maybe formed at an emulsification temperature of from about 10° C. to about130° C. and in certain embodiments from about 50° C. to about 100° C.

In general, the monomers will include from about 20% to about 97% byweight of the oil phase at least one substantially water-insolublemonofunctional alkyl acrylate or alkyl methacrylate. For example,monomers of this type may include C4-C18 alkyl acrylates and C2-C18methacrylates, such as ethylhexyl acrylate, butyl acrylate, hexylacrylate, octyl acrylate, nonyl acrylate, decyl acrylate, isodecylacrylate, tetradecyl acrylate, benzyl acrylate, nonyl phenyl acrylate,hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonylmethacrylate, decyl methacrylate, isodecyl methacrylate, dodecylmethacrylate, tetradecyl methacrylate, and octadecyl methacrylate.

The oil phase may also have from about 2% to about 40%, and in certainembodiments from about 10% to about 30%, by weight of the oil phase, asubstantially water-insoluble, polyfunctional crosslinking alkylacrylate or methacrylate. This crosslinking comonomer, or crosslinker,is added to confer strength and resilience to the resulting HIPE foam.Examples of crosslinking monomers of this type may have monomerscontaining two or more activated acrylate, methacrylate groups, orcombinations thereof. Nonlimiting examples of this group include1,6-hexanedioldiacrylate, 1,4-butanedioldimethacrylate,trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,1,12-dodecyldimethacrylate, 1,14-tetradecanedioldimethacrylate, ethyleneglycol dimethacrylate, neopentyl glycol diacrylate(2,2-dimethylpropanediol diacrylate), hexanediol acrylate methacrylate,glucose pentaacrylate, sorbitan pentaacrylate, and the like. Otherexamples of crosslinkers contain a mixture of acrylate and methacrylatemoieties, such as ethylene glycol acrylate-methacrylate and neopentylglycol acrylate-methacrylate. The ratio of methacrylate:acrylate groupin the mixed crosslinker may be varied from 50:50 to any other ratio asneeded.

Any third substantially water-insoluble comonomer may be added to theoil phase in weight percentages of from about 0% to about 15% by weightof the oil phase, in certain embodiments from about 2% to about 8%, tomodify properties of the HIPE foams.

“Toughening” monomers may be desired which impart toughness to theresulting HIPE foam. These include monomers such as styrene, vinylchloride, vinylidene chloride, isoprene, and chloroprene. Without beingbound by theory, it is believed that such monomers aid in stabilizingthe HIPE during polymerization (also known as “curing”) to provide amore homogeneous and better formed HIPE foam which results in bettertoughness, tensile strength, abrasion resistance, and the like. Monomersmay also be added to confer flame retardancy as disclosed in U.S. Pat.No. 6,160,028 (Dyer) issued Dec. 12, 2000. Monomers may be added toconfer color, for example vinyl ferrocene, fluorescent properties,radiation resistance, opacity to radiation, for example leadtetraacrylate, to disperse charge, to reflect incident infrared light,to absorb radio waves, to form a wettable surface on the HIPE foamstruts, or for any other desired property in a HIPE foam. In some cases,these additional monomers may slow the overall process of conversion ofHIPE to HIPE foam, the tradeoff being necessary if the desired propertyis to be conferred. Thus, such monomers can be used to slow down thepolymerization rate of a HIPE. Examples of monomers of this type canhave styrene and vinyl chloride.

The oil phase may further contain an emulsifier used for stabilizing theHIPE. Emulsifiers used in a HIPE can include: (a) sorbitan monoesters ofbranched C16-C24 fatty acids; linear unsaturated C16-C22 fatty acids;and linear saturated C12-C14 fatty acids, such as sorbitan monooleate,sorbitan monomyristate, and sorbitan monoesters, sorbitan monolauratediglycerol monooleate (DGMO), polyglycerol monoisostearate (PGMIS), andpolyglycerol monomyristate (PGMM); (b) polyglycerol monoesters of-branched C16-C24 fatty acids, linear unsaturated C16-C22 fatty acids,or linear saturated C12-C14 fatty acids, such as diglycerol monooleate(for example diglycerol monoesters of C18:1 fatty acids), diglycerolmonomyristate, diglycerol monoisostearate, and diglycerol monoesters;(c) diglycerol monoaliphatic ethers of -branched C16-C24 alcohols,linear unsaturated C16-C22 alcohols, and linear saturated C12-C14alcohols, and mixtures of these emulsifiers. See U.S. Pat. No. 5,287,207(Dyer et al.), issued Feb. 7, 1995 and U.S. Pat. No. 5,500,451 (Goldmanet al.) issued Mar. 19, 1996. Another emulsifier that may be used ispolyglycerol succinate (PGS), which is formed from an alkyl succinate,glycerol, and triglycerol.

Such emulsifiers, and combinations thereof, may be added to the oilphase so that they can have between about 1% and about 20%, in certainembodiments from about 2% to about 15%, and in certain other embodimentsfrom about 3% to about 12% by weight of the oil phase. Coemulsifiers mayalso be used to provide additional control of cell size, cell sizedistribution, and emulsion stability, particularly at highertemperatures, for example greater than about 65° C. Examples ofcoemulsifiers include phosphatidyl cholines and phosphatidylcholine-containing compositions, aliphatic betaines, long chain C12-C22dialiphatic quaternary ammonium salts, short chain C1-C4 dialiphaticquaternary ammonium salts, long chain C12-C22dialkoyl(alkenoyl)-2hydroxyethyl, short chain C1-C4 dialiphaticquaternary ammonium salts, long chain C12-C22 dialiphatic imidazoliniumquaternary ammonium salts, short chain C1-C4 dialiphatic imidazoliniumquaternary ammonium salts, long chain C12-C22 monoaliphatic benzylquaternary ammonium salts, long chain C12-C22dialkoyl(alkenoyl)-2-aminoethyl, short chain C1-C4 monoaliphatic benzylquaternary ammonium salts, short chain C1-C4 monohydroxyaliphaticquaternary ammonium salts. Ditallow dimethyl ammonium methyl sulfate(DTDMAMS) may be used as a coemulsifier.

The oil phase may comprise a photoinitiator at between about 0.05% andabout 10%, and in certain embodiments between about 0.2% and about 10%by weight of the oil phase. Lower amounts of photoinitiator allow lightto better penetrate the HIPE foam, which can provide for polymerizationdeeper into the HIPE foam. However, if polymerization is done in anoxygen-containing environment, there should be enough photoinitiator toinitiate the polymerization and overcome oxygen inhibition.Photoinitiators can respond rapidly and efficiently to a light sourcewith the production of radicals, cations, and other species that arecapable of initiating a polymerization reaction. The photoinitiatorsused in the present invention may absorb UV light at wavelengths ofabout 200 nanometers (nm) to about 800 nm, in certain embodiments about200 nm to about 350 nm. If the photoinitiator is in the oil phase,suitable types of oil-soluble photoinitiators include benzyl ketals,a-hydroxyalkyl phenones, a-amino alkyl phenones, and acylphospineoxides. Examples of photoinitiators include2,4,6-[trimethylbenzoyldiphosphine]oxide in combination with2-hydroxy-2-methyl-1-phenylpropan-1-one (50:50 blend of the two is soldby Ciba Speciality Chemicals, Ludwigshafen, Germany as DAROCUR® 4265);benzyl dimethyl ketal (sold by Ciba Geigy as IRGACURE 651);a-,a-dimethoxy-a-hydroxy acetophenone (sold by Ciba Speciality Chemicalsas DAROCUR® 1173); 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (sold by Ciba SpecialityChemicals as IRGACURE® 907); 1-hydroxycyclohexyl-phenyl ketone (sold byCiba Speciality Chemicals as IRGACURE® 184);bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (sold by CibaSpeciality Chemicals as IRGACURE 819); diethoxyacetophenone, and4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-methylpropyl) ketone (sold byCiba Speciality Chemicals as IRGACURE® 2959); and Oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (sold byLambeth spa, Gallarate, Italy as ESACURE® KIP EM.

The dispersed aqueous phase of a HIPE can have water, and may also haveone or more components, such as initiator, photoinitiator, orelectrolyte, wherein in certain embodiments, the one or more componentsare at least partially water soluble.

One component of the aqueous phase may be a water-soluble electrolyte.The water phase may contain from about 0.2% to about 40%, in certainembodiments from about 2% to about 20%, by weight of the aqueous phaseof a water-soluble electrolyte. The electrolyte minimizes the tendencyof monomers, comonomers, and crosslinkers that are primarily oil solubleto also dissolve in the aqueous phase. Examples of electrolytes includechlorides or sulfates of alkaline earth metals such as calcium ormagnesium and chlorides or sulfates of alkali earth metals such assodium. Such electrolyte can include a buffering agent for the controlof pH during the polymerization, including such inorganic counterions asphosphate, borate, and carbonate, and mixtures thereof. Water solublemonomers may also be used in the aqueous phase, examples being acrylicacid and vinyl acetate.

Another component that may be present in the aqueous phase is awater-soluble free-radical initiator. The initiator can be present at upto about 20 mole percent based on the total moles of polymerizablemonomers present in the oil phase. The initiator may be present in anamount of from about 0.001 to about 10 mole percent based on the totalmoles of polymerizable monomers in the oil phase. Suitable initiatorsinclude ammonium persulfate, sodium persulfate, potassium persulfate,2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, and othersuitable azo initiators. To reduce the potential for prematurepolymerization which may clog the emulsification system, addition of theinitiator to the monomer phase may be just after or near the end ofemulsification.

Photoinitiators present in the aqueous phase may be at least partiallywater soluble and can have between about 0.05% and about 10%, and incertain embodiments between about 0.2% and about 10% by weight of theaqueous phase. Lower amounts of photoinitiator allow light to betterpenetrate the HIPE foam, which can provide for polymerization deeperinto the HIPE foam. However, if polymerization is done in anoxygen-containing environment, there should be enough photoinitiator toinitiate the polymerization and overcome oxygen inhibition.Photoinitiators can respond rapidly and efficiently to a light sourcewith the production of radicals, cations, and other species that arecapable of initiating a polymerization reaction. The photoinitiatorsused in the present invention may absorb UV light at wavelengths of fromabout 200 nanometers (nm) to about 800 nm, in certain embodiments fromabout 200 nm to about 350 nm, and in certain embodiments from about 350nm to about 450 nm. If the photoinitiator is in the aqueous phase,suitable types of water-soluble photoinitiators include benzophenones,benzils, and thioxanthones. Examples of photoinitiators include2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride;2,2′-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dehydrate;2,2′-Azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride;2,2′-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide]; 2,2′-Azobis(2-methylpropionamidine)dihydrochloride;2,2′-dicarboxymethoxydibenzalacetone,4,4′-dicarboxymethoxydibenzalacetone,4,4′-dicarboxymethoxydibenzalcyclohexanone,4-dimethylamino-4′-carboxymethoxydibenzalacetone; and4,4′-disulphoxymethoxydibenzalacetone. Other suitable photoinitiatorsthat can be used in the present invention are listed in U.S. Pat. No.4,824,765 (Sperry et al.) issued Apr. 25, 1989.

In addition to the previously described components other components maybe included in either the aqueous or oil phase of a HIPE. Examplesinclude antioxidants, for example hindered phenolics, hindered aminelight stabilizers; plasticizers, for example dioctyl phthalate, dinonylsebacate; flame retardants, for example halogenated hydrocarbons,phosphates, borates, inorganic salts such as antimony trioxide orammonium phosphate or magnesium hydroxide; dyes and pigments;fluorescers; filler pieces, for example starch, titanium dioxide, carbonblack, or calcium carbonate; fibers; chain transfer agents; odorabsorbers, for example activated carbon particulates; dissolvedpolymers; dissolved oligomers; and the like.

The heterogeneous mass comprises enrobeable elements and discrete piecesof foam. The enrobeable elements may be a web such as, for example,nonwoven, a fibrous structure, an air-laid web, a wet laid web, a highloft nonwoven, a needlepunched web, a hydroentangled web, a fiber tow, awoven web, a knitted web, a flocked web, a spunbond web, a layeredspunbond melt blown web, a carded fiber web, a coform web of cellulosefiber and melt blown fibers, a coform web of staple fibers and meltblown fibers, and layered webs that are layered combinations thereof.

The enrobeable elements may be, for example, conventional absorbentmaterials such as creped cellulose wadding, fluffed cellulose fibers,wood pulp fibers also known as airfelt, and textile fibers. Theenrobeable elements may also be fibers such as, for example, syntheticfibers, thermoplastic particulates or fibers, tricomponent fibers, andbicomponent fibers such as, for example, sheath/core fibers having thefollowing polymer combinations: polyethylene/polypropylene,polyethylvinyl acetate/polypropylene, polyethylene/polyester,polypropylene/polyester, copolyester/polyester, and the like. Theenrobeable elements may be any combination of the materials listed aboveand/or a plurality of the materials listed above, alone or incombination. The enrobeable elements may be hydrophobic or hydrophilic.The enrobeable elements may be treated to be made hydrophobic. Theenrobeable elements may be treated to become hydrophilic.

The constituent fibers of the heterogeneous mass can be comprised ofpolymers such as polyethylene, polypropylene, polyester, and blendsthereof. The fibers can be spunbound fibers. The fibers can be meltblownfibers. The fibers can comprise cellulose, rayon, cotton, or othernatural materials or blends of polymer and natural materials. The fiberscan also comprise a super absorbent material such as polyacrylate or anycombination of suitable materials. The fibers can be monocomponent,bicomponent, and/or biconstituent, non-round (e.g., capillary channelfibers), and can have major cross-sectional dimensions (e.g., diameterfor round fibers) ranging from 0.1-500 microns. The constituent fibersof the nonwoven precursor web may also be a mixture of different fibertypes, differing in such features as chemistry (e.g. polyethylene andpolypropylene), components (mono- and bi-), denier (micro denier and >20denier), shape (i.e. capillary and round) and the like. The constituentfibers can range from about 0.1 denier to about 100 denier.

In one aspect, known absorbent web materials in an as-made can beconsidered as being homogeneous throughout. Being homogeneous, the fluidhandling properties of the absorbent web material are not locationdependent, but are substantially uniform at any area of the web.Homogeneity can be characterized by density, basis weight, for example,such that the density or basis weight of any particular part of the webis substantially the same as an average density or basis weight for theweb. By the apparatus and method of the present invention, homogeneousfibrous absorbent web materials are modified such that they are nolonger homogeneous, but are heterogeneous, such that the fluid handlingproperties of the web material are location dependent. Therefore, forthe heterogeneous absorbent materials of the present invention, atdiscrete locations the density or basis weight of the web may besubstantially different than the average density or basis weight for theweb. The heterogeneous nature of the absorbent web of the presentinvention permits the negative aspects of either of permeability orcapillarity to be minimized by rendering discrete portions highlypermeable and other discrete portions to have high capillarity.Likewise, the tradeoff between permeability and capillarity is managedsuch that delivering relatively higher permeability can be accomplishedwithout a decrease in capillarity.

The heterogeneous mass may also include superabsorbent material thatimbibe fluids and form hydrogels. These materials are typically capableof absorbing large quantities of body fluids and retaining them undermoderate pressures. The heterogeneous mass can include such materialsdispersed in a suitable carrier such as cellulose fibers in the form offluff or stiffened fibers. The heterogeneous mass may includethermoplastic particulates or fibers. The materials, and in particularthermoplastic fibers, can be made from a variety of thermoplasticpolymers including polyolefins such as polyethylene (e.g., PULPEX®) andpolypropylene, polyesters, copolyesters, and copolymers of any of theforegoing.

Depending upon the desired characteristics, suitable thermoplasticmaterials include hydrophobic fibers that have been made hydrophilic,such as surfactant-treated or silica-treated thermoplastic fibersderived from, for example, polyolefins such as polyethylene orpolypropylene, polyacrylics, polyamides, polystyrenes, and the like. Thesurface of the hydrophobic thermoplastic fiber can be renderedhydrophilic by treatment with a surfactant, such as a nonionic oranionic surfactant, e.g., by spraying the fiber with a surfactant, bydipping the fiber into a surfactant or by including the surfactant aspart of the polymer melt in producing the thermoplastic fiber. Uponmelting and resolidification, the surfactant will tend to remain at thesurfaces of the thermoplastic fiber. Suitable surfactants includenonionic surfactants such as Brij 76 manufactured by ICI Americas, Inc.of Wilmington, Del., and various surfactants sold under the Pegosperse®trademark by Glyco Chemical, Inc. of Greenwich, Conn. Besides nonionicsurfactants, anionic surfactants can also be used. These surfactants canbe applied to the thermoplastic fibers at levels of, for example, fromabout 0.2 to about 1 g. per sq. of centimeter of thermoplastic fiber.

Suitable thermoplastic fibers can be made from a single polymer(monocomponent fibers), or can be made from more than one polymer (e.g.,bicomponent fibers). The polymer comprising the sheath often melts at adifferent, typically lower, temperature than the polymer comprising thecore. As a result, these bicomponent fibers provide thermal bonding dueto melting of the sheath polymer, while retaining the desirable strengthcharacteristics of the core polymer.

Suitable bicomponent fibers for use in the present invention can includesheath/core fibers having the following polymer combinations:polyethylene/polypropylene, polyethylvinyl acetate/polypropylene,polyethylene/polyester, polypropylene/polyester, copolyester/polyester,and the like. Particularly suitable bicomponent thermoplastic fibers foruse herein are those having a polypropylene or polyester core, and alower melting copolyester, polyethylvinyl acetate or polyethylene sheath(e.g., DANAKLON®, CELBOND® or CHISSO® bicomponent fibers). Thesebicomponent fibers can be concentric or eccentric. As used herein, theterms “concentric” and “eccentric” refer to whether the sheath has athickness that is even, or uneven, through the cross-sectional area ofthe bicomponent fiber. Eccentric bicomponent fibers can be desirable inproviding more compressive strength at lower fiber thicknesses. Suitablebicomponent fibers for use herein can be either uncrimped (i.e. unbent)or crimped (i.e. bent). Bicomponent fibers can be crimped by typicaltextile means such as, for example, a stuffer box method or the gearcrimp method to achieve a predominantly two-dimensional or “flat” crimp.

The length of bicomponent fibers can vary depending upon the particularproperties desired for the fibers and the web formation process.Typically, in an airlaid web, these thermoplastic fibers have a lengthfrom about 2 mm to about 12 mm long such as, for example, from about 2.5mm to about 7.5 mm long, and from about 3.0 mm to about 6.0 mm long.Nonwoven fibers may be between 5 mm long and 75 mm long, such as, forexample, 10 mm long, 15 mm long, 20 mm long, 25 mm long, 30 mm long, 35mm long, 40 mm long, 45 mm long, 50 mm long, 55 mm long, 60 mm long, 65mm long, or 70 mm long. The properties-of these thermoplastic fibers canalso be adjusted by varying the diameter (caliper) of the fibers. Thediameter of these thermoplastic fibers is typically defined in terms ofeither denier (grams per 9000 meters) or decitex (grams per 10,000meters). Suitable bicomponent thermoplastic fibers as used in an airlaidmaking machine can have a decitex in the range from about 1.0 to about20 such as, for example, from about 1.4 to about 10, and from about 1.7to about 7 decitex.

The compressive modulus of these thermoplastic materials, and especiallythat of the thermoplastic fibers, can also be important. The compressivemodulus of thermoplastic fibers is affected not only by their length anddiameter, but also by the composition and properties of the polymer orpolymers from which they are made, the shape and configuration of thefibers (e.g., concentric or eccentric, crimped or uncrimped), and likefactors. Differences in the compressive modulus of these thermoplasticfibers can be used to alter the properties, and especially the densitycharacteristics, of the respective thermally bonded fibrous matrix.

The heterogeneous mass can also include synthetic fibers that typicallydo not function as binder fibers but alter the mechanical properties ofthe fibrous webs. Synthetic fibers include cellulose acetate, polyvinylfluoride, polyvinylidene chloride, acrylics (such as Orlon), polyvinylacetate, non-soluble polyvinyl alcohol, polyethylene, polypropylene,polyamides (such as nylon), polyesters, bicomponent fibers, tricomponentfibers, mixtures thereof and the like. These might include, for example,polyester fibers such as polyethylene terephthalate (e.g., DACRON® andKODEL®), high melting crimped polyester fibers (e.g., KODEL® 431 made byEastman Chemical Co.) hydrophilic nylon (HYDROFIL®), and the like.Suitable fibers can also hydrophilized hydrophobic fibers, such assurfactant-treated or silica-treated thermoplastic fibers derived from,for example, polyolefins such as polyethylene or polypropylene,polyacrylics, polyamides, polystyrenes, polyurethanes and the like. Inthe case of nonbonding thermoplastic fibers, their length can varydepending upon the particular properties desired for these fibers.Typically they have a length from about 0.3 to 7.5 cm, such as, forexample from about 0.9 to about 1.5 cm. Suitable nonbondingthermoplastic fibers can have a decitex in the range of about 1.5 toabout 35 decitex, such as, for example, from about 14 to about 20decitex. However structured, the total absorbent capacity of theheterogeneous mass containing foam pieces should be compatible with thedesign loading and the intended use of the mass. For example, when usedin an absorbent article, the size and absorbent capacity of theheterogeneous mass may be varied to accommodate different uses such asincontinence pads, pantiliners, regular sanitary napkins, or overnightsanitary napkins. The heterogeneous mass can also include other optionalcomponents sometimes used in absorbent webs. For example, a reinforcingscrim can be positioned within the respective layers, or between therespective layers, of the heterogeneous mass.

The heterogeneous mass comprising open-cell foam pieces produced fromthe present invention may be used as an absorbent core or a portion ofan absorbent core in absorbent articles, such as feminine hygienearticles, for example pads, pantiliners, and tampons; disposablediapers; incontinence articles, for example pads, adult diapers;homecare articles, for example wipes, pads, towels; and beauty carearticles, for example pads, wipes, and skin care articles, such as usedfor pore cleaning.

The heterogeneous mass may be used as an absorbent core for an absorbentarticle. The absorbent core may be relatively thin, less than about 5 mmin thickness, or less than about 3 mm, or less than about 1 mm inthickness. Cores having a thickness of greater than 5 mm are alsocontemplated herein. Thickness can be determined by measuring thethickness at the midpoint along the longitudinal centerline of theabsorbent structure by any means known in the art for doing while undera uniform pressure of 0.25 psi. The absorbent core can compriseabsorbent gelling materials (AGM), including AGM fibers, as is known inthe art.

The heterogeneous mass may be formed or cut to a shape, the outer edgesof which define a periphery. Additionally, the heterogeneous mass may becontinuous such that it may be rolled or wound upon itself, with orwithout the inclusion of preformed cut lines demarcating theheterogeneous mass into preformed sections. When used as an absorbentcore, the shape of the heterogeneous mass can be generally rectangular,circular, oval, elliptical, or the like. Absorbent core can be generallycentered with respect to the longitudinal centerline and transversecenterline of an absorbent article. The profile of absorbent core can besuch that more absorbent is disposed near the center of the absorbentarticle. For example, the absorbent core can be thicker in the middle,and tapered at the edges in a variety of ways known in the art.

Applicants have found that the absorbent structure may exhibitincreasing compressive energy through a usage cycle. The heterogeneousmass exhibits a compressive energy (measured in millijoules (mJ)) whenwet representing between 100% and up to 200% of the dry compressiveenergy, such as, for example, between 100% and 180%, between 110% and170%, between 120% and 160%, between 125% and 150%, or between 130% and150%. This surprising result allows one to create a product that is neargarment-like when dry that changes during use such that the articleincreases in compressive energy when wet.

The dry compressive energy is between 10% and 99% of the wet compressiveenergy measurement such as, for example, between 15% and 80%, between20% and 75%, between 25% and 70%, such as, for example, 30%, 35%, 40%,45%, 50%, 60%, or 65% of the wet compressive energy measurement. The wetcompressive energy is calculated when the sample is loaded with 7 ml of10% saline solution.

Recovery energy is an indicator of how well a core/product can retain orregain is original shape to offer a larger area of coverage to theproduct-to-body interface—more specifically the amount of work thecore/product will perform against the consumer's body and garment. Theupper limit for recovery energy should be the 1_(st) Cycle CompressiveEnergy in the dry state. The fifth cycle recovery energy, as measured bythe bunched compression test, may be used as measure of the product whenit is in use. Testing it in a dry state and a wet state allows one tosee how the absorbent structure reacts while being used before and afterfluid is absorbed by the product.

Without being bound by theory, Applicants have found that compressive &recovery energies, peak force, and core/product caliper are allimportant components that exhibit how an absorbent product will fit,feel and protect—each components of this ratio will be discussed toexplain its role in regards to delivering these benefits.

As previously stated, the peak force is an indicator of the flexibilityof the absorbent structure. Without being bound by theory, Applicantshave found that a lower peak force allows an absorbent product to bemore “garment like”. When balanced with the appropriate fifth cycleRecovery Energy range according to the bunched compression test, aproduct may be “garment like” and still capable of retaining its shapeduring use without creating bunching or comfort issues for the consumer.The 1^(st) cycle compressive energy, as measured by the bunchedcompression test, is a measure of the effort required to “break-in” theproduct—for it to more naturally conform and fit to her body. The upperlimit for recovery energy should be the 1^(st) Cycle Compressive Energyin the dry state—it is preferred that this energy approaches the upper

RE 5th PF 1st PERCENT Cycle Cycle CALIPER DIFF Sample (mJ) (Grams) mmCALIPER Invention A DRY 1.5 69.88 1.79  23% Invention A WET 2.11 82.962.2   Invention B DRY 0.98 56.68 3.77   3% Invention B WET 0.64 65.993.9   Invention C DRY 1.39 77.59 3.29  13% Invention C WET 1.01 98.363.72 Invention D DRY 0.78 45.14 1.39 149% Invention D WET 1.01 83.263.44 Prior Art E DRY 0.07 19.84 1.69 202% Prior Art E WET 1.12 61.435.11 Prior Art F DRY 2.88 177.85 1.24  44% Prior Art F WET 0.62 105.691.78   Prior Art G DRY 3.58 170.15 2.29  18% Prior Art G WET 2.86 156.862.7compressive energy limit without sacrificing the resultant comfort ofthe core/product.

The table above lists several examples of inventions that exhibit thedesired properties

(Invention A-Invention D). Invention A-C represent examples of aheterogeneous mass enrobed by open cell foam. Inventions B-C haveundergone additional solid state formation. Invention D represents animproved core system using AGM. Prior Art E-G represent currentlyavailable absorbent structures in the market including a traditionalHIPE core layer structure (Prior Art G).

Applicants have found that the desired product are able to exhibit thedesired properties in 15 use while having a caliper change of less than200% combined with a 1st cycle dry peak force (PF) of between 30 and 150grams, and a 5th cycle dry recovery energy of between 0.1 mJ and 2.8 mJ.The caliper change may be between 1% and 200%, between 10% and 100%, orbetween 20% and 80%. The absorbent structures may exhibit a fifth cyclerecovery energy for a dry cycle that is between 0.1 mJ and 2.8 mJ, suchas, for example, 0.2 mJ and 2.5 mJ, 0.5 mJ and 2.0 mJ, 20 or 0.9 mJ and1.5 mJ. Applicants have found that having a fifth dry cycle recoveryenergy between 0.1 mJ and 2.8 mJ represents improved recovery during useallowing products to maintain sufficient structure while still beingflexible and garment like. Applicants have found that absorbentstructures that exhibit a first cycle peak force for a dry cycle that isbetween 30 and 150 grams have sufficient flexibility and the minimumnecessary level of structure. The absorbent structures may exhibit afirst cycle peak force for a dry cycle that is between 30 and 150 grams,such as, for example, between 40 and 120 grams, between 45 and 100grams, or between 50 and 80 grams. Core caliper is a highly consumerrelevant indicator of how garment or panty-like an absorbent articlewill be when worn due to its connection to flexibility and bulk. Acore/product with less caliper occupies less space at the panty-to-bodyinterface and is more flexible i.e. can more freely move as the pantywould naturally.

As shown in Table 1(Invention examples B-C), one can affect the materialthrough the use of solid state formation, such as, for example, ringrolling. Formation means known for deforming a generally planar fibrousweb into a three-dimensional structure are utilized in the presentinvention to modify as-made absorbent materials into absorbent materialshaving relatively higher permeability without a significantcorresponding decrease in capillary pressure. Formation means maycomprise a pair of inter-meshing rolls, typically steel rolls havinginter-engaging ridges or teeth and grooves. However, it is contemplatedthat other means for achieving formation can be utilized, such as thedeforming roller and cord arrangement disclosed in US 2005/0140057published Jun. 30, 2005. Therefore, all disclosure of a pair of rollsherein is considered equivalent to a roll and cord, and a claimedarrangement reciting two inter-meshing rolls is considered equivalent toan inter-meshing roll and cord where a cord functions as the ridges of amating inter-engaging roll. The pair of intermeshing rolls of theinstant invention may be considered as equivalent to a roll and aninter-meshing element, wherein the inter-meshing element can be anotherroll, a cord, a plurality of cords, a belt, a pliable web, or straps.Likewise, other known formation technologies, such as creping,necking/consolidation, corrugating, embossing, button break, hot pinpunching, and the like are believed to be able to produce absorbentmaterials having some degree of relatively higher permeability without asignificant corresponding decrease in capillary pressure. Formationmeans utilizing rolls include “ring rolling”, a “SELF” or “SELF'ing”process, in which SELF stands for Structural Elastic Like Film, as“micro-SELF”, and “rotary knife aperturing” (RKA); as described in U.S.Pat. No. 7,935,207 Zhao et al., granted May 3, 2011. Other referencesrelated to formation means include U.S. Pat. No. 6,203,654 McFall etal., granted Mar. 20, 2001 and U.S. Pat. No. 6,410,820 McFall et al.,granted Jun. 25, 2002. The heterogeneous mass exhibits an increasingcompression energy during a usage cycle. The heterogeneous mass mayexhibit a change in energy from a 1st cycle and a 20th cycle that isless than 50% of the initial energy of the 1st cycle. The heterogeneousmass exhibits a change in compression energy from dry to wet that isless than 20% of the initial dry energy.

As shown in the table above, the heterogeneous mass (Inventions A-C)exhibits a 5^(th) cycle Recovery Energy of between 0.9 mJ and 2 mJ, suchas for example, 0.98, 1.1, 1.2, 1.3, 1.4, and 1.5 mJ.

The absorbent structure may serve as any portion of an absorbentarticle. The absorbent structure may serve as the absorbent core of anabsorbent article. The absorbent structure may serve as a portion of theabsorbent core of an absorbent article. More than one absorbentstructure may be combined wherein each absorbent structure differs fromat least one other absorbent structure in either the choice ofenrobeable elements or by a characteristic of its open-cell foam pieces.The different two or more absorbent structures may be combined to forman absorbent core. The absorbent article may further comprise a topsheetand a backsheet.

The absorbent structure may be used as a topsheet for an absorbentarticle. The absorbent structure may be combined with an absorbent coreor may only be combined with a backsheet.

The absorbent structure may be combined with any other type of absorbentlayer such as, for example, a layer of cellulose, a layer comprisingsuperabsorbent gelling materials, a layer of absorbent airlaid fibers,or a layer of absorbent foam. Other absorbent layers not listed arecontemplated herein.

The absorbent structure may be utilized by itself for the absorption offluids without placing it into an absorbent article.

An absorbent article may comprise a liquid pervious topsheet. Thetopsheet suitable for use herein can comprise wovens, non-wovens, and/orthree-dimensional webs of a liquid impermeable polymeric film comprisingliquid permeable apertures. The topsheet for use herein can be a singlelayer or may have a multiplicity of layers. For example, thewearer-facing and contacting surface can be provided by a film materialhaving apertures which are provided to facilitate liquid transport fromthe wearer facing surface towards the absorbent structure. Such liquidpermeable, apertured films are well known in the art. They provide aresilient three-dimensional fibre-like structure. Such films have beendisclosed in detail for example in U.S. Pat. Nos. 3,929,135, 4,151,240,4,319,868, 4,324,426, 4,343,314, 4,591,523, 4,609,518, 4,629,643,4,695,422 or WO 96/00548. The absorbent articles of FIGS. 1 to 17comprising embodiments of the absorbent structure can also comprise abacksheet and a topsheet. The backsheet may be used to prevent thefluids absorbed and contained in the absorbent structure from wettingmaterials that contact the absorbent article such as underpants, pants,pyjamas, undergarments, and shirts or jackets, thereby acting as abarrier to fluid transport. The backsheet may also allow the transfer ofat least water vapour, or both water vapour and air through it.

Especially when the absorbent article finds utility as a sanitary napkinor panty liner, the absorbent article can be also provided with a pantyfastening means, which provides means to attach the article to anundergarment, for example a panty fastening adhesive on the garmentfacing surface of the backsheet. Wings or side flaps meant to foldaround the crotch edge of an undergarment can be also provided on theside edges of the napkin.

FIG. 1 is a plan view of a sanitary napkin 10 comprising a topsheet 12,a backsheet (not shown), an absorbent core 16 located between thetopsheet 12 and the backsheet, a longitudinal axis 24, and a transverseaxis 26. The absorbent core 16 comprises of a heterogeneous mass 18comprising elements 30 and one or more discrete foam pieces 20 thatenrobe the at least one element 30 of the heterogeneous mass 18. Asshown in FIG. 1 the elements 30 are fibers 22. A portion of the topsheetis cut out in order to show underlying portions.

FIGS. 2 and 3 are cross sections of pad shown in FIG. 1, cut through the2-2 vertical plane along the longitudinal axis 24 and cut through the3-3 vertical plane along the transverse axis 26, respectively. As can beseen in FIGS. 2 and 3, the absorbent core 16 is between the topsheet 12and the backsheet 14. As shown in the embodiment of FIGS. 2 and 3, thediscrete foam pieces 20 are spread out throughout the absorbent core andenrobe the elements 30 of the heterogeneous mass 18. The discrete pieces20 of foam may extend beyond the enrobeable elements to form part of theouter surface of the heterogeneous mass. Additionally, discrete piecesof foam may be fully intertwined within the heterogeneous mass of theabsorbent core. Voids 28 containing gas are located between the fibers22.

FIG. 4 is a plan view of a sanitary napkin 10 illustrating an embodimentof the invention. The sanitary napkin 10 comprises a topsheet 12, abacksheet (not shown), an absorbent core 16 located between the topsheet12 and the backsheet, a longitudinal axis 24, and a transverse axis 26.The absorbent core 16 comprises of a heterogeneous mass 18 comprisingelements 30 and one or more discrete foam pieces 20 that enrobe the atleast one element 30 of the heterogeneous mass 18. As shown in FIG. 4,the elements 30 are fibers 22. A portion of the topsheet is cut out inorder to show underlying portions. As shown in FIG. 4 the discrete foampieces 20 may be continuous along an axis of the heterogeneous mass,such as, for example, the longitudinal axis. Further, the discrete foam20 may be arranged to form a line in the heterogeneous mass. Thediscrete foam pieces 20 are shown proximate to the top of theheterogeneous mass 18 but may also be located at any vertical height ofthe heterogeneous mass 18 such that enrobeable elements 30 may belocated above and below the one or more of the discrete foam pieces 20.FIGS. 5, 6 and 7 are cross sections of the pad shown in FIG. 4, cutthrough the 5-5, the 66, and the 7-7 vertical planes, respectively. The5-5 vertical plane is parallel to the transverse axis of the pad and the6-6 and 7-7 vertical planes are parallel to the longitudinal axis. Ascan be seen in FIGS. 5 to 7, the absorbent core 16 is between thetopsheet 12 and the backsheet 14. As shown in the embodiment of FIG. 5,the discrete foam pieces 20 are spread out throughout the absorbent coreand enrobe the elements 30 of the heterogeneous mass 18. As shown inFIG. 6, a discrete foam piece 20 may be continuous and extend along theheterogeneous mass. As shown in FIG. 7, the heterogeneous mass may nothave any discrete foam pieces along a line cross section of theabsorbent core. Voids 28 containing gas are located between the fibers22.

FIG. 8 is a zoomed in view of a portion of FIG. 5 indicated on FIG. 5 bya dotted line circle 80. As shown in FIG. 8, the heterogeneous mass 18comprises discreet foam pieces 20 and enrobeable elements 30 in the formof fibers 22. Voids 28 containing gas are located between the fibers 22.

FIG. 9 is a plan view of a sanitary napkin 10 illustrating an embodimentof the invention. The sanitary napkin 10 comprises a topsheet 12, abacksheet (not shown), an absorbent core 16 located between the topsheet12 and the backsheet, a longitudinal axis 24, and a transverse axis 26.The absorbent core 16 comprises of a heterogeneous mass 18 comprisingelements 30 and one or more discrete foam pieces 20 that enrobe the atleast one element 30 of the heterogeneous mass 18. As shown in FIG. 9,the elements 30 are fibers 22. A portion of the topsheet is cut out inorder to show underlying portions. As shown in FIG. 9, the discrete foampieces 20 may form a pattern, such as, for example, a checkerboard grid.

FIGS. 10 and 11 are cross sections of the pad shown in FIG. 9, cutthrough the 10-10 and 11-11 vertical planes, respectively. As can beseen in FIGS. 10 and 11, the absorbent core 16 is between the topsheet12 and the backsheet 14. As shown in the embodiment of FIGS. 10 and 11,the discrete foam pieces 20 are spread out throughout the absorbent coreand enrobe the elements 30 in the form of fibers 22 of the heterogeneousmass 18. Voids 28 containing gas are located between the fibers 22.FIGS. 12 to 16 are SEM micrographs of HIPE foam pieces 20 intertwinedwithin a heterogeneous mass 18 comprising nonwoven fibers 22. FIG. 12shows a SEM micrograph taken at 15× magnification. As shown in FIG. 12,a discrete HIPE foam piece 20 and the elements 30 in the form of fibers22 are intertwined. The HIPE foam piece 20 enrobes one or more of thefibers 22 of the heterogeneous mass 18. The fibers 22 of theheterogeneous mass 18 cross through the HIPE foam piece 20. Voids 28containing gas are located between fibers 22.

FIG. 13 shows the absorbent core of FIG. 12 at a magnification of 50×.As shown in FIG. 13, the HIPE foam pieces 20 envelop a portion of one ormore fibers 22 such that the fibers bisect through the HIPE foam pieces20. The HIPE foam pieces 20 enrobe the fibers such that the pieces arenot free to move about within the absorbent core. As shown in FIG. 13,vacuoles 32 may exist within the enrobing foam 20. Vacuoles 32 maycontain a portion of the enrobeable element 30.

FIG. 14 shows another SEM micrograph of a cross section of a discreteHIPE foam piece taken at 15× magnification. As shown in FIG. 14, theHIPE foam piece 20 may extend beyond the elements 30 of theheterogeneous mass 18 to form a portion of the outer surface of theheterogeneous mass 18. The HIPE foam pieces 20 enrobes one or more ofthe fibers 22 of the heterogeneous mass 18. The fibers of the absorbentcore cross through the HIPE foam piece. Voids 28 containing gas arelocated between fibers 22.

FIG. 15 shows another SEM micrograph of a heterogeneous mass 18 taken ata magnification of 18×. As shown in FIG. 15, the HIPE foam pieces 20 maybe positioned below the outer surface of the heterogeneous mass 18 suchthat it does not form part of the outer surface of the heterogeneousmass 18 and is surrounded by fibers 22 and voids 28 containing gas. Oneor more vacuoles 32 may be formed within the foam piece 20.

FIG. 16 shows a SEM micrograph of the heterogeneous mass of FIG. 15taken at a magnification of 300×. As shown in FIG. 16, the heterogeneousmass 18 has an open-cell foam piece 20 that enrobes one or moreenrobeable elements 30 in the form of fibers 22. As shown in FIG. 16,vacuoles 32 may exist within the enrobing foam 20. Vacuoles 32 maycontain a portion of the enrobeable element 30. As shown in the figure,the vacuoles 32 have a cross-sectional surface area that is between1.0002 and 900,000,000 times the cross-sectional surface area of thefibers 22 or between 1.26 and 9,000,000 times the cross-sectionalsurface area of the cells 36 in the open-cell foam piece 20. FIG. 17 isa photographic image of a heterogeneous mass 18 having enrobeableelements 30 comprising a nonwoven web and open-cell foam pieces 20enrobing the enrobeable elements 30. As seen in the photographic image,the open-cell foam pieces are discrete along at least one of thelateral, longitudinal, or vertical axis of the heterogeneous mass. Asseen in FIG. 17, the discrete open-cell foam pieces may form a patternwhen viewed from above by a user.

-   A. An absorbent structure comprising one or more absorbent layers    wherein the absorbent structure exhibits a first cycle Peak Force    compression between about 30 grams and about 150 grams; wherein the    absorbent structure further exhibits a fifth cycle dry recovery    energy between 0.1 mJ and 2.8 mJ.-   B. The absorbent structure according to paragraph A, wherein the    absorbent structure exhibits a fifth cycle wet recovery energy    between 0.6 mJ and 5.0 mJ.-   C. The absorbent structure according to paragraph A or B, wherein    the absorbent structure caliper change from Dry to Wet is between 0%    and 175%.-   D. The absorbent structure according to any of paragraphs A-C,    wherein the absorbent structure exhibits an increase in Peak Force    during a first cycle when measured from dry to wet.-   E. The absorbent structure according to any of paragraphs A-D,    wherein the absorbent structure comprises less than 30% fibers by    volume.-   F. An absorbent article comprising the absorbent structure according    to any of paragraphs A-E.

G. The absorbent structure according to any of paragraphs A-D, whereinthe absorbent structure comprises a layer of absorbent polymer material.

-   H. The absorbent structure according to paragraph G, wherein the    layer of absorbent polymer material has a basis weight of less than    250 g/m².-   I. The absorbent structure according to any of paragraphs A-H,    wherein one or more layers of the absorbent structure are    substantially free of cellulose fibers.-   J. The absorbent structure according to any of paragraphs A-I,    wherein the absorbent structure comprises a heterogeneous mass.-   K. The absorbent structure according to paragraph J, wherein the    heterogeneous mass comprises at least 5% of discrete open cell foam    pieces for a fixed volume.-   L. The absorbent structure according to any of paragraphs J-K,    wherein the heterogeneous mass comprises enrobeable elements    selected from the group consisting of creped cellulose wadding,    fluffed cellulose fibers, wood pulp fibers also known as airfelt,    textile fibers, synthetic fibers, rayon fibers, airlaid, absorbent    fibers thermoplastic particulates or fibers, tricomponent fibers,    bicomponent fibers, tufts, a nonwoven, a fibrous structure, an    air-laid web, a wet laid web, a high loft nonwoven, a needlepunched    web, a hydroentangled web, a fiber tow, a woven web, a knitted web,    a flocked web, a spunbond web, a layered spunbond/melt blown web, a    carded fiber web, a coform web of cellulose fiber and melt blown    fibers, a coform web of staple fibers and melt blown fibers, layered    webs and combinations thereof.-   M. The absorbent structure according to any of paragraphs J-L,    wherein the heterogeneous mass comprises between 10% and 99% of gas    for a fixed volume.-   N. The absorbent structure according to paragraph K, wherein the    discrete open cell foam pieces comprise HIPE foam.-   O. The absorbent structure according to paragraph K, wherein the    discrete open cell foam pieces are continuous along at least one of    the longitudinal axis and the lateral axis.-   P. An absorbent structure comprising one or more absorbent layers    wherein the absorbent structure exhibits a first cycle Peak Force    compression between about 30 grams and about 150 grams; wherein the    absorbent structure further exhibits a fifth cycle dry recovery    energy between 0.1 mJ and 2.8 mJ; and wherein the absorbent    structure exhibits a fifth cycle wet recovery energy between 0.6 mJ    and 5.0 mJ.-   Q. The absorbent structure according to paragraph P, wherein the    absorbent structure caliper change from Dry to Wet is between 0% and    175%.-   R. The absorbent structure according to paragraph P or Q, wherein    the absorbent structure exhibits an increase in Peak Force during a    first cycle when measured from dry to wet.-   S. The absorbent structure according to any of paragraphs P-R,    wherein the absorbent structure comprises a layer of absorbent    polymer material.-   T. The absorbent structure according to any of paragraphs P-S,    wherein the absorbent structure comprises a heterogeneous mass.    Method for Assessing Areas for Pore Size Calculations Using SEM    Imaging:    Sample Preparation

The first step is to prepare the sample to be imaged using SEM: Sectionof the heterogeneous mass are cut into approximately 1.5 cm×4 cm stripsfrom the original samples. These strips are then cut the strips intosections. Each section should contain the entire composite. The stripsshould be cut using a razor blade, such as VWR Single Edge Industrial,0.009″ thick surgical carbon steel or equivalent, at room temperature(available from VWR Scientific, Radnor, Pa. USA). Following the cuttingof strips into sections, the sections are adhered to a mount usingdouble-side Cu tape, with the-sectioned face up, and sputter Au coated.

Analysis

Secondary Electron (SE) images are obtained using an SEM, such as a FEIQuanta 450 (available from FEI Company, Hillsboro, Oreg., USA), operatedin high-vacuum mode using acceleration voltages between 3 and 5 kV and aworking distance of approximately 12-18 mm.

This methodology assumes the analyst is skilled in SEM operation so thatimages with sufficient contrast are obtained.

Viewing the SEM Sample

Samples should be viewed at 25 or 50× magnification. The differentpore-size ranges are distinguished by the different portions within theheterogeneous mass. Distinct portions exhibit different cell/poresizes/open area/solid phase vs gas phase. The magnification for theportions is chosen to enable clear visualization of the portion and theability to distinguish the solid phase from the gas phase.

Determination of portions having different pore-size ranges is done at amagnification of 25×. The heterogeneous mass SEM is divided into anupper portion and a lower portion at the point where the lowest fiber islocated along the Z-direction. Each portion is then divided into threeportions. This creates three portions with the first upper portion andthe first lower portion sharing a boundary. The pore-size range of theupper second portion is compared to pore-size range of the lower secondportion. The lower third region may be compared to the upper secondregion and the lower second region to determine if there is anadditional pore-size range. The upper third region may be compared tothe upper second region and the lower second region to determine ifthere is an additional pore-size range. Pore size ranges are determinedon the largest ten pores in the field of view and using software that iscapable of analyzing the SEM images.

Bunch Compression Test

Bunched Compression of a sample is measured on a constant rate ofextension tensile tester (a suitable instrument is the MTS Allianceusing Testworks 4.0 software, as available from MTS Systems Corp., EdenPrairie, Minn., or equivalent) using a load cell for which the forcesmeasured are within 10% to 90% of the limit of the cell. All testing isperformed in a room controlled at 23° C.±3C° and 50%±2% relativehumidity. The test can be performed wet or dry.

The bottom stationary fixture 3000 consists of two matching sampleclamps 3001 each 100 mm wide each mounted on its own movable platform3002 a, 3002 b. The clamp has a “knife edge” 3009 that is 110 mm long,which clamps against a 1 mm thick hard rubber face 3008 (as shown inFIG. 18). When closed, the clamps are flush with the interior side ofits respective platform. The clamps are aligned such that they hold anun-bunched specimen horizontal and orthogonal to the pull axis of thetensile tester. The platforms are mounted on a rail 3003 which allowsthem to be moved horizontally left to right and locked into position.The rail has an adapter 3004 compatible with the mount of the tensiletester capable of securing the platform horizontally and orthogonal tothe pull axis of the tensile tester. The upper fixture 2000 is acylindrical plunger 2001 having an overall length of 70 mm with adiameter of 25.0 mm. The contact surface 2002 is flat with no curvature.The plunger 2001 has an adapter 2003 compatible with the mount on theload cell capable of securing the plunger orthogonal to the pull axis ofthe tensile tester.

Samples are conditioned at 23° C.±3C° and 50%±2% relative humidity forat least 2 hours before testing. When testing a whole article, removethe release paper from any panty fastening adhesive on the garmentfacing side of the article. Lightly apply talc powder to the adhesive tomitigate any tackiness. If there are cuffs, excise them with scissors,taking care not to disturb the top sheet of the product. Place thearticle, body facing surface up, on a bench. On the article identify theintersection of the longitudinal midline and the lateral midline. Usinga rectangular cutting die, cut a specimen 100 mm in the longitudinaldirection by 80 mm in the lateral direction, centered at theintersection of the midlines. When testing just the absorbent body of anarticle, place the absorbent body on a bench and orient as it will beintegrated into an article, i.e., identify the body facing surface andthe lateral and longitudinal axis. Using a rectangular cutting die, cuta specimen 100 mm in the longitudinal direction by 80 mm in the lateraldirection, centered at the intersection of the midlines. The specimencan be analyzed both wet and dry. The dry specimen requires no furtherpreparation. The wet specimens are dosed with one of two test solutions:10.00 mL±0.01 mL of a 0.9% w/v saline solution (i.e., 9.0 g of NaCldiluted to 1 L deionized water) or 7.00 mL±0.01 mL 10% w/v salinesolution (100.0 g of NaCl diluted to 1 L deionized water). The dose isadded using a calibrated Eppendorf-type pipettor, spreading the fluidover the complete body facing surface of the specimen within a period ofapproximately 3 sec. The wet specimen is tested 15.0 min±0.1 min afterthe dose is applied.

Program the tensile tester to zero the load cell, then lower the upperfixture at 2.00 mm/sec until the contact surface of the plunger touchesthe specimen and 0.02 N is read at the load cell. Zero the crosshead.Program the system to lower the crosshead 15.00 mm at 2.00 mm/sec thenimmediately raise the crosshead 15.00 mm at 2.00 mm/sec. This cycle isrepeated for a total of five cycles, with no delay between cycles. Datais collected at 100 Hz during all compression/decompression cycles.

Position the left platform 3002 a 2.5 mm from the side of the upperplunger (distance 3005). Lock the left platform into place. Thisplatform 3002 a will remain stationary throughout the experiment. Alignthe right platform 3002 b 50.0 mm from the stationary clamp (distance3006). Raise the upper probe 2001 such that it will not interfere withloading the specimen. Open both clamps. Referring to FIG. 19a , placethe specimen with its longitudinal edges (i.e., the 100 mm long edges)within the clamps. With the specimen laterally centered, securely fastenboth edges. Referring to FIG. 19b , move the right platform 3002 btoward the stationary platform 3002 a a distance 20.0 mm Allow thespecimen to bow upward as the movable platform is positioned. Manuallylower the probe 2001 until the bottom surface is approximately 1 cmabove the top of the bowed specimen.

Start the test and collect displacement (mm) verses force (N) data forall five cycles. Construct a graph of Force (N) versus displacement (mm)separately for all cycles. A representative curve is shown in FIG. 20a .From the curve record the Maximum Compression Force for each Cycle tothe nearest 0.01N. Calculate the % Recovery between the First and Secondcycle as (TD-E2)/(TD-E1)*100 where TD is the total displacement and E2is the extension on the second compression curve that exceeds 0.02 N.Record to the nearest 0.01%. In like fashion calculate the % Recoverybetween the First Cycle and other cycles as (TD-Ei)/(TD-E1)*100 andreport to the nearest 0.01%. Referring to FIG. 20b , calculate theEnergy of Compression for Cycle 1 as the area under the compressioncurve (i.e., area A+B) and record to the nearest 0.1 mJ. Calculate theEnergy Loss from Cycle 1 as the area between the compression anddecompression curves (i.e., Area A) and report to the nearest 0.1 mJ.Calculate the Energy of Recovery for Cycle 1 as the area under thedecompression curve (i.e. Area B) and report to the nearest 0.1 mJ. Inlike fashion calculate the Energy of Compression (mJ), Energy Loss (mJ)and

Energy of Recovery (mJ) for each of the other cycles and record to thenearest 0.1 mJ For each sample, analyze a total of five (5) replicatesand report the arithmetic mean for each parameter. All results arereported specifically as dry or wet including test fluid (0.9% or 10%).

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Values disclosed herein as ends of ranges are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each numerical range is intended to meanboth the recited values and any integers within the range. For example,a range disclosed as “1 to 10” is intended to mean “1, 2, 3, 4, 5, 6, 7,8, 9, and 10.”

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A sanitary napkin, having a longitudinal axis anda transverse axis and comprising an absorbent core structure comprisingone or more absorbent layers, the one or more absorbent layerscomprising a heterogeneous mass, the heterogeneous mass comprising anonwoven web of fibers and a plurality of discrete open cell foam piecesenrobing fibers within the nonwoven web, wherein the discrete open cellfoam pieces are present and distributed among the fibers of the nonwovenweb across and within at least a central region of the napkin occupyingan intersection of the longitudinal axis and the transverse axis, andwherein the absorbent core structure exhibits a first cycle Peak Forcecompression between about 30 grams and about 150 grams; wherein theabsorbent structure further exhibits a fifth cycle dry recovery energybetween 0.1 mJ and 2.8 mJ.
 2. The sanitary napkin of claim 1, whereinthe absorbent core structure exhibits a fifth cycle wet recovery energybetween 0.6 mJ and 5.0 mJ.
 3. The sanitary napkin of claim 1, whereinthe absorbent core structure caliper change from Dry to Wet is between0% and 175%.
 4. The sanitary napkin of claim 1, wherein the absorbentcore structure exhibits an increase in Peak Force during a first cyclewhen measured from dry to wet.
 5. The sanitary napkin of claim 1,wherein the absorbent core structure comprises less than 30% fibers byvolume.
 6. The sanitary napkin according to claim 1, wherein theabsorbent core structure comprises a layer of absorbent polymermaterial.
 7. The sanitary napkin according to claim 6, wherein the layerof absorbent polymer material has a basis weight of less than 250 g/m².8. The sanitary napkin of claim 1, wherein one or more layers of theabsorbent core structure are substantially free of cellulose fibers. 9.The sanitary napkin of claim 1, wherein the heterogeneous mass comprisesat least 5% of discrete open cell foam pieces for a fixed volume. 10.The sanitary napkin of claim 9, wherein the discrete open cell foampieces comprise HIPE foam.
 11. The sanitary napkin of claim 9, whereinthe discrete open cell foam pieces are continuous along at least one ofthe longitudinal axis and the transverse axis.
 12. The sanitary napkinof claim 1, wherein the heterogeneous mass comprises enrobeable elementsselected from the group consisting of creped cellulose wadding, fluffedcellulose fibers, wood pulp fibers also known as airfelt, textilefibers, synthetic fibers, rayon fibers, airlaid, absorbent fibersthermoplastic particulates or fibers, tricomponent fibers, bicomponentfibers, tufts, a nonwoven, a fibrous structure, an air-laid web, a wetlaid web, a high loft nonwoven, a needlepunched web, a hydroentangledweb, a fiber tow, a woven web, a knitted web, a flocked web, a spunbondweb, a layered spunbond/melt blown web, a carded fiber web, a coform webof cellulose fiber and melt blown fibers, a coform web of staple fibersand melt blown fibers, layered webs and combinations thereof.
 13. Thesanitary napkin of claim 1, wherein the heterogeneous mass comprisesbetween 10% and 99% of gas for a fixed volume.
 14. A sanitary napkin,having a longitudinal axis and a transverse axis and comprising anabsorbent core structure comprising one or more absorbent layers, theone or more absorbent layers comprising a heterogeneous mass, theheterogeneous mass comprising a nonwoven web of fibers and a pluralityof discrete open cell foam pieces enrobing fibers within the nonwovenweb, wherein the discrete open cell foam pieces are present anddistributed among the fibers of the nonwoven web across and within atleast a central region of the napkin occupying an intersection of thelongitudinal axis and the transverse axis, and wherein the absorbentcore structure exhibits a first cycle Peak Force compression betweenabout 30 grams and about 150 grams; wherein the absorbent core structurefurther exhibits a fifth cycle dry recovery energy between 0.1 mJ and2.8 mJ; and wherein the absorbent structure exhibits a fifth cycle wetrecovery energy between 0.6 mJ and 5.0 mJ.
 15. The sanitary napkin ofclaim 14, wherein the absorbent structure caliper change from Dry to Wetis between 0% and 175%.
 16. The sanitary napkin of claim 14, wherein theabsorbent core structure exhibits an increase in Peak Force during afirst cycle when measured from dry to wet.
 17. The sanitary napkinaccording to claim 14, wherein the absorbent structure comprises a layerof absorbent polymer material.